Phytoliths In Woody Plants From the Miombo Woodlands of Mozambique

Tim  Bennett

Fossil macroplants and phytoliths occur in the sediments of the palaeoanthropological site of Olduvai Gorge, northern Tanzania. Current research on hominin land use in the Basin during the Plio–Pleistocene has a strong palaeoenvironmental emphasis on the palaeovegetation in particular. The occurrence of macroplants and phytoliths at Olduvai, and their usefulness and reliability for palaeovegetation interpretation are assessed here for the first time. Modern reference collections from analogous environments have been established and used to identify the fossil taxa from the eastern palaeolake margin of Lowermost Bed II as the test case for very detailed spatially and temporally constrained vegetation reconstruction. Fourier Transform Infrared Spectrometry (FTIR) analysis was used to identify the minerals of the fossil sediments. Modern plants produce more phytoliths than are preserved in the fossil soils but there were sufficient numbers to show diverse and changing vegetation over short time periods Silicified macroplant fragments of sedge culms and dicot stems occur with phytoliths, but do not always represent the same plant taxa. A more complex flora was shown when using both forms of fossil plants. During Lowermost bed II times, at the locality of FLKN monocots and dicots occurred, indicating the presence of marshland and grassland after the deposition of Tuff IF. At VEK, the phytoliths indicate a shift in dominance from dicots to monocots to a mixture of the two and including palms. At HWKEE, initially palms dominated then there was a mixture of palms, grasses and dicots. The vegetation at MCK comprised dicots, monocots sedges and grasses. This detailed vegetation data complements the more broad scale vegetation interpretations that have been deduced from the pollen, isotopes and faunal data sets.

The archaeological site of Klasies River is famous for the richness of its Middle Stone Age deposits, which offer the opportunity to document behaviors of early modern humans in Africa, as well as the paleo-environmental context of their occupation of the area during the late Pleistocene. The Main Site deposits (dated to ca. 115 to 55 ka) include botanical remains such as seeds and charcoal, which suggests that micro-plant particles like phytoliths could also have been deposited. Yet, no phytolith reference collection based on both modern plant and soil material has been produced for Klasies River, which complicates attempts of phytolith analysis of the site's deposits. One of our challenges was therefore to initiate a new and comprehensive phytolith reference collection of modern plants and soils occurring today in the vicinity of Klasies. For this purpose, we processed phytoliths from 24 modern plant specimens and 16 soil samples from different vegetation patches, all located today in a perimeter <5 km 2 around the Main Site. Our analyses indicate that ovate/orbicular and/or tabular polygonal phytoliths are the most recurrent and abundant morphotypes (>53% and up to 94%) produced in the leaf tissues of the Anacardiaceae, Aster-aceae, Celastraceae, Ericaceae, Proteaceae, and Vitaceae species we studied, which are all eudicotyle-doneous taxa. Regarding the Cyperaceae, Restionaceae, and one of the Proteaceae species (Leucadendron spissifolium, a fynbos shrub), they each produce distinct phytolith assemblages: the Restionaceae leaf/ culm assemblage is dominated by psilate and decorated globular/spheroid phytoliths (94%), whereas the Cyperaceae leaf/culm content and the Proteaceae leaf content are both dominated by silicified papillae (like) bodies (54% and 63%, respectively). Besides, both globular/spheroid and papillae (like) phytoliths account for 34% and 8% in the fynbos soil collected. Our analyses also show that ovate/orbicular and/or polygonal phytoliths occur in very small amounts (<2%) in modern soils of the area although they are numerous in most of the eudicotyledoneous leaf tissues we analyzed. Conversely, grass silica short cell phytoliths are found abundantly in the soils collected in close proximity to the Main Site (>66%), where grasses do however occur sparsely in the current vegetation.

South Africa continues to receive substantial attention from scholars researching modern human origins. The importance of this region lies in the many caves and rock shelters containing well preserved evi- dence of human activity, cultural material complexity and a growing number of early modern human fossils dating to the Middle Stone Age (MSA). South Africa also hosts the world's smallest floral kingdom, now called the Greater Cape Floristic Region (GCFR), with high species richness and endemism. In paleoanthropological research, improving our capacity to reconstruct past climatic and environmental conditions can help us to shed light on survival strategies of hunteregatherers. To do this, one must use actualistic studies of modern assemblages from extant habitats to develop analogies for the past and improve paleoenvironmental reconstructions. Here, we present a phytolith study of modern surface soil samples from different GCFR vegetation types of the south coast of South Africa. In this study, the phytolith concentration and morphological distribution are related to the physicochemical properties of soils, the environmental conditions and the characterization of the vegetation for the different study areas. Our results show that phytolith concentration relates mostly to vegetation types and the dominant vegetation rather than to the type of soils. More abundant phytoliths from Restionaceae and woody/ shrubby vegetation are also noted from fynbos vegetation and grass phytoliths are a recurrent compo- nent in all the vegetation types in spite of being a minor component in the modern vegetation. The grass silica short cells from these plants, however, suggest a mix of C3 and C4 grasses in most of the vegetation types with a major presence of the rondels ascribed to C3 grasses. The exceptions are riparian, coastal thicket and coastal forest vegetation, which are characterized by the dominance of C4 grass phytoliths.

Annals of Botany 104: 91 –113, 2009 doi:10.1093/aob/mcp097, available online at www.aob.oxfordjournals.org Phytoliths in woody plants from the Miombo woodlands of Mozambique Julio Mercader1,*, Tim Bennett1, Chris Esselmont2, Steven Simpson1 and Dale Walde1 1 Department of Archaeology, University of Calgary, 2500 University Drive N.W., Calgary, Alberta, T2N 1N4, Canada and 2 Environics Research Group, 999 8 Street S.W., Calgary, Alberta, T2R 1J5, Canada Received: 23 February 2009 Returned for revision: 17 March 2009 Accepted: 19 March 2009 Published electronically: 9 May 2009 † Background and Aims There are no descriptions of phytoliths produced by plants from the ‘Zambezian’ zone, where Miombo woodlands are the dominant element of the largest single phytochorion in sub-Saharan Africa. The preservation of phytoliths in fossil records of Africa makes phytoliths a tool to study early plant communities. Paleo-ethnobotanical interpretation of phytoliths relies on the comparison of ancient types with morphotypes extracted from living reference collections. † Methods Phytoliths were extracted from plant samples representing 41 families, 77 genera and 90 species through sonic cleaning, dry ashing and acid treatment; and phytoliths thus extracted were quantified. For each species, an average of 216 phytoliths were counted. The percentage of each morphotype identified per species was calculated, and types were described according to the descriptors from the International Code for Phytolith Nomenclature. Phytolith assemblages were subject to discriminant analysis, cluster analysis and principal component analysis. † Key Results Phytoliths were grouped into 57 morphotypes (two were articulated forms and 55 were discrete shapes), and provide a reference collection of phytolith assemblages produced by Miombo woody species. Common and unique morphotypes are described and taxonomic and grouping variables are looked into from a statistical perspective. † Conclusions The first quantitative taxonomy of phytoliths from Miombos is presented here, including new types and constituting the most extensive phytolith key for any African ecoregion. Evidence is presented that local woody species are hypervariable silica producers and their phytolith morphotypes are highly polymorphic. The taxonomic significance of these phytoliths is largely poor, but there are important exceptions that include the morphotypes produced by members from .10 families and orders. The typical phytolithic signal that would allow scientists to identify ancient woodlands of ‘Zambezian’ affiliation comprises only half of the original number of phytoliths originally produced and might favour the more resilient blocky, cylindroid, globular and tabular forms. Key words: Africa, Mozambique, Niassa, Miombo, phytolith analysis, reference collection, quantitative methods, principal component analysis, cluster analysis, discriminant analysis. IN T RO DU C T IO N Monosilicic acid [Si(OH)4] exists in a solute, monomeric state over a large part of the Earth’s surface (Iler, 1979). It abounds in soils, where plants take it up through the roots, and distribute it as one of several sap constituents to shoots and leaves by means of the transpiration stream (Lewin and Reimann, 1969). With increasing concentrations in the sap, silicic acid combines chemically with other monomers to produce a network molecule, a polymerized silica gel (SiO2), that in some families can reach concentrations of .10 % of the plant’s dry weight (Epstein, 1994). At the nanometre level, the gel solidifies inside and between cells as both amorphous and discretely shaped silica bodies called phytoliths (Snyder et al., 2007). In many species, these noncrystalline, bio-mineralized silica precipitates are a major mineral plant constituent (Epstein, 1994), but not all plants produce them. Phytoliths have a specific gravity of 1.5 – 2.3, are highly polymorphic, have the same optical properties in all directions and a refractive index of 1.4 (Elbaum et al., 2003). Depending on the extent of carbon coating, phytoliths * For correspondence. E-mail Mercader@ucalgary.ca may be clear, brown-pigmented or even totally opaque (Prychid et al., 2004). Phytolith production varies greatly among different genotypes of the same plant species and plant part (Epstein, 1999). With some exceptions, lower phylogenetic orders produce more phytoliths, although it is known that many basal monocots are non-producers (Prychid et al., 2004) and, contrarily, that some of the most derived clades produce high numbers of phytoliths (Hodson et al., 2005). After plants die and decompose, the silica phytoliths contained in their tissues revert back to the soil. With death, the biogenic silica assemblage thus released suffers the insults of time, decay and differential preservation. As a result, over the course of several decades and plant generations, soils will contain a time-averaged, polygenic and biased record of local vegetation (Strömberg, 2004), not a floristical composition snapshot (see Thorn, 2008, p. 30 for an example of disagreement between soil phytolith assemblages and the overlying vegetation that grows on the spot at the time of sampling). Yet, phytoliths are helpful indicators of general plant physiognomy and the ecosystem’s structure (Piperno, 2006) both today (Barboni et al., 2007) and in the past (Strömberg et al., 2007). Although phytolith studies have # The Author 2009. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org 92 Mercader et al. — Phytoliths from woody plants in Mozambique been carried out in modern soils from Central Africa (Runge 1999), West Africa (Bremond et al., 2005) and East Africa (Shahack-Gross et al., 2003, 2004; Albert et al., 2006; Bremond et al., 2008), quantitative work on silica bodies from living African plants is scarce and focuses on grasses from two phytochoria north of the equator (White, 1983): the Somalia-Masai (Palmer and Tucker, 1983) and the Sudano-Sahelian (Fahmy, 2008) vegetation zones. An extremely small amount of qualitative information is also known about the phytoliths produced by some African trees and bushes from the Guineo-Congolian region (Runge and Runge, 1997). The preservation of phytoliths in terrestrial and lacustrine sediments from the African Miocene (Retallack, 1992), Plio-Pleistocene (Barboni et al., 1999; Albert et al., 2006) and Late Quaternary (Alexandre et al., 1997; Mercader et al., 2000) makes them a promising tool to study ancient plant communities. However, paleo-ethnobotanical interpretation relies on actualistic comparisons with silica morphotypes from modern plants (e.g. Gallego and Distel, 2004; Wallis, 2003; Carnelli et al., 2004; Honaine et al., 2006; Tsartsidou et al., 2007) and, therefore, a good understanding of the phytolith production of modern plants is a prerequisite for such studies. In this article, we estimate biogenic silica production by African woody species from the Miombo woodlands of the Niassa province of northwestern Mozambique, and present a reference collection for a wide range of woody plants growing today along the Niassa Rift. In particular, we determine the taxonomic significance of phytolith types produced by indigenous trees and shrubs from this part of Africa, and hypothesize the phytolithic signal that ‘Zambezian’ plants would leave behind in the geological and archaeological record. Virtually no modern phytoliths have been identified in the richest and most diversified flora and vegetation on the continent (White, 1983, p. 89), the Zambezian zone, where Miombo woodlands are the dominant element of the largest single phytochorion in sub-Saharan Africa. The total number of taxa in the Flora Zambesiaca is estimated at approx. 11 400, of which Mozambique possesses half (Timberlake, et al., 2006, pp. 751, 754). Miombo woodlands typically display a single storey stand with a discontinuous tree canopy and an underlying sparse layer of small trees, shrubs, sedges and helyophytic grasses (Campbell et al., 1996). In mature Miombos, 95– 98 % of the above-ground biomass is comprised of woody plants (Frost, 2006, p. 22). When these woodlands suffer alteration, the tree to grass ratio changes drastically. Bloesch and Mbago (2006) estimate that the canopy cover in moderately modified settings is 40 %, and others claim that in disturbed Miombos the grass biomass surpasses that from the woody component (Ribeiro et al., 2008). Most of the vegetation is briefly deciduous, but, depending on precipitation, some areas support totally deciduous and evergreen plants. White (1983, p. 93) classified Miombo woodlands into ‘wetter’ (.1000 mm of rainfall) and ‘drier’ Miombos (,1000 mm), and the study area supports both. Niassa’s woodlands intersperse with other formations; namely (a) semi-evergreen forest; (b) savannas; and (c) hydromorphic grasslands known as ‘dambos’ or ‘mbungas’. This complex scenario of divergent influences is homogenized by the conspicuous dominance of trees from one genus only: Brachystegia (Bloesch and Mbago, 2006, p. 8), although, to a much a lesser extent, it may be co-dominant with Julbernardia. It is this dominance by the subfamily Caesalpinioideae (Fabaceae) that gives both floristic coherence and uniform physiognomy to the Miombo ecoregion (Exell et al., 1960; White, 1983; Frost, 1996). The study area (Fig. 1) comprises the escarpment flanking the Lake Niassa Rift at an altitude of 465 m a.s.l. and the adjacent highlands (1841 m a.s.l.), which represents the third highest elevation in Mozambique. The districts where our work was conducted (Lago and Sanga) belong to the ‘Lichinga-Cobue’ geological unit (Lächelt, 2004) comprising two stocks: the crystalline basement and the Proterozoic cover with granodiorite, granosyenite, granites, and diverse gneisses and paragneisses (Lächelt, 2004). In the lowlands, red soils are shallow, neutral and they have a silty sand texture (classified as Ferric Lixisols by FAO, 1998; Instituto Nacional de Investigação Agronómica, 1995). In the highlands, red clayey soils have alkaline to acidic pH, and are deep and oxic (also known as Rhodic Ferralsols; FAO, E 34.50º N TANZANIA Lake Niassa MOZAMBIQUE Province of Niassa Metangula S 12.40º Njawala Botanical transect 100 km Lake Niassa MALAWI 1841 m Njawala a.s.l. 465 m a.s.l. Lake Niassa Relief map Metangula Altitudinal cross-section Transect length: 50 km F I G . 1. Study area in northern Mozambique, the location of the botanical transect carried out, and altitudinal cross-section. Mercader et al. — Phytoliths from woody plants in Mozambique 1998). The mean annual rainfall ranges from 700 mm in the lake-bordering lowlands by Lake Niassa to 1400 mm in the adjacent highlands (Gama, 1990, pp. 31– 33). The precipitation system is unimodal, with a copious rainy season that lasts 5 months (January – May) and a severe, drought-prone season from June to December. M AT E R I A L S A N D M E T H O D S From the available sources, we have compiled a list of the 65 most common genera of vascular plants for the province of Niassa (Table 1; Gama, 1990; da Silva et al., 2004; Timberlake et al., 2004; Ribeiro et al., 2008; Bloesch and Mbago, 2006) so that, by comparison with our list of specimens processed (see Supplementary Data, available online), the reader has a measure of the overall ecological coverage and representativeness achieved in this study. The majority of our samples were field-collected by our crew around two loci: Metangula (Lago district, lowlands) and Njawala (Sanga district, highlands; Fig. 1). We targeted all trees and shrubs that our indigenous collectors were able to sample within a radius of 5 km. Botanical specimens were taken at the end of their annual growing cycle, during the dry season, to ensure better phytolith build up in their tissues. For the sake of completeness, when a species was unavailable to us, but it was estimated to be important for our phytolith work, specimens taken from past collections of ours carried out in neighbouring regions and countries since 1993 were used instead. In other cases, samples were obtained from the largest herbarium in sub-Saharan Africa (Pretoria). To identify woody taxa we relied on (a) the expertise of several local collectors; (b) the plant names given to our samples by these collectors; (c) the direct experience with the local flora acquired by our group over the course of five field seasons; (d ) the comparison with keys from the standard field guides (Palgrave, 2002; Burrows and Willis, 2005); (e) the taxonomic dictionaries of local plant names mentioned above; and ( f ) the identifications provided by the Pretoria Herbarium. Our botanical nomenclature is that of the index of accepted names and synonyms from the ‘Checklist of flowering plants of Sub-Saharan Africa’ (Klöpper et al., 2006). We secured vernacular names through collaboration with five bush doctors over the course of five field seasons, and, to the best of our knowledge, we collected samples from .90 % of the flora most frequently employed by the Yao and Nyanja collectives from Niassa for building, cooking, clothing, medicinal and ritual purposes. Nine specimens bear indigenous names which do not appear in the existing ethnobotanies by Watt et al. (1962), Binns (1972), Jansen and Mendes (1990), Gama (1990), De Koning (1993), Morris (1996), Williamson (2005) and Fowler (2007), and therefore are presented here for the first time. Whenever taxonomic identification was not possible, we have used instead the plant name in Chinyanja/Yao languages. Otherwise, a specimen appears listed as ‘unknown’. Phytolith extraction from botanical samples followed the dry ashing methodology outlined by Albert and Weiner (2001; cf. Parr et al., 2001), with minor modifications. All specimens 93 TA B L E 1. List of common plants in the province of Niassa, Northern Mozambique Family Anacardiaceae Annonaceae Annonaceae Apocynaceae Apocynaceae Apocynaceae Arecaceae Asteraceae Bignoniaceae Bignoniaceae Bombacaceae Chrysobalanaceae Combretaceae Combretaceae Cyperaceae Dipterocarpaceae Ebenaceae Euphorbiaceae Euphorbiaceae Euphorbiaceae Euphorbiaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Fabaceae Flaucortiaceae Melastomataceae Moraceae Moraceae Myrtaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Poaceae Polygalaceae Proteaceae Proteaceae Rubiaceae Kirkaceae Sterculiaceae Strychnaceae Tamaricaceae Velloziacea Verbenaceae Genus Sclerocarya Annona Xylopia Diplorhynchus Landolphia Voacanga Hyphaene Aspilia Kigelia Stereospermum Adansonia Parinari Combretum Terminalia Cyperus Monotes Diospyros Antidesma Euphorbia Pseudolachnostylis Uapaca Acacia Afzelia Albizia Brachystegia Burkea Cordyla Dalbergiella Dichrostachys Entada Erythrophleum Lonchocarpus Pericopsis Piliogstigma Pterocarpus Flaucortia Khaya Ficus Treculia Syzygium Andropogon Aristida Eragrostis Hyparrhenia Hyperthelia Loudetia Melinis Miscanthus Oxytenanthera Panicum Pennisetum Phragmites Sporobulus Themeda Urochlaena Securidaca Faurea Protea Vangueria Kirkia Sterculia Strychnos Tamarix Vellozia Vitex 94 Mercader et al. — Phytoliths from woody plants in Mozambique TA B L E 2. Phytolith taxonomy for arboreal taxa from Miombo ecosystems: code, name, descriptors, totals and their frequency ( %) in the assemblage Number Morphotype Descriptors n % 1 2 3 Blocky Blocky cavate Blocky corniculate 483 4 12 0.02370 0.00020 0.00059 5a– n 5o 5b 4 5 Blocky facetate Blocky hairy 1 9 0.00005 0.00044 5q 5r 6 Blocky pilate 88 0.00432 5s 7 8 9 10 11 12 13 14 668 56 7 38 94 137 616 9 0.03278 0.00314 0.00034 0.02502 0.00461 0.00672 0.03023 0.00044 5t 5u 5v 5w 5x 2a 2b, c 2r 10 52 7 6 0.00049 0.00255 0.00034 0.00029 2d 2e 2j 2f 2 0.00010 2g Thin epidermal cells with puzzle-like outline. Variable textures Tabular, sub-polygonal body covered with layers Thin epidermal polygonal cells. Variable textures 651 1 4945 0.03194 0.00005 0.24264 2h, i 3x, y 2k–o Single-cell, fluid-conducting tissue Spheroid beset with prickles Large spheroid beset with prickles 2133 677 122 0.10466 0.03322 0.00599 3a, b 3c 3d Facetate spheroid/hemisphere Sub-spheroid with extended, thickened rim Spheroid with granular texture Large spheroid with granular texture 5 368 1616 91 0.00025 0.01806 0.07929 0.00447 3g, h 3i–n 3o 3q 63 0.00309 3t 1924 41 0.09441 0.00201 3b, u 3v Spheroid with pitted texture 170 0.00834 3e, f Large spheroid beset with nodular processes 105 0.00515 3r, s 26 0.00128 6n Ovate with psilate texture Cubic body, orbicular to square in outline, with adaxial bisection and psilate texture Hemispheric body with rugose to sulcate texture 10 2 106 0.00049 0.00010 0.00520 3z, aa 3ae 3ab 39 Blocky polygonal Blocky radiating Blocky trapezoid Blocky tuberculate Clavate granulate Cylindroid Cylindroid bulbous Cylindroid columellate Cylindroid crenate Cylindroid lacunate Cylindroid large Cylindroid reticulate Cylindroid scrobiculate Epidermal jig-saw Epidermal laminate Epidermal polygonal Epidermal tracheid Globular echinate Globular echinate large Globular facetate Globular folded Globular granulate Globular granulate large Globular granulate oblong Globular psilate Globular psilate large Globular scrobiculate Globular tuberculate Globular verrucate oblong Globulose Globulose bisected Lenticular concave/ convex Shield Block with lacunose/slightly scrobiculate texture Block with psilate texture and centric depression Ovate, rectangular, polygonal or irregular block with corniculate projections. Variable textures Faceted, psilate block Ovate, rectangle, polygonal or irregular block with irregular/scrobiculate texture; long pointed projections Orbicular, oblong, rectangle, polygonal or irregular block with scrobiculate texture and projections that have straight or slightly curved ends Polygonal/irregular block with a psilate/scrobiculate texture Orbicular to rectangular block with a surface covered by concentric layers Trapezoid block with lacunose texture Irregular block with lacunose/scrobiculate/tuberculate texture Club-shaped body with granular texture Small cylindroid mostly with a psilate texture Cylindroid/renate with a psilate texture and irregular bulbuous enlargements Very large cylindroid with surface covered by processes 3 0.00015 3af, ag 40 41 Spooliform Stomata/hair/base Tabular to trapezoidal body with one side curved and the other one wavy. Psilate to scrobiculate texture. Rim is bevelled Cylindroid body with mesial strangulation Stomatal complex, hairs and hair bases 70 3454 0.00343 0.16948 42 43 44 45 46 47 48 Tabular corniculate Tabular crenate Tabular elongate Tabular facetate Tabular lanceolate Tabular oblong Tabular psilate Elongate parallelepiped with corniculate texture Tabular body with psilate texture and scalloped edges Elongate Facetate with partly psilate and partly corniculate textures Large tabular, psilate body shaped like a spear Large tabular body with orbicular, ovate or oblong outline and psilate texture Elongate to oblong body with psilate texture 16 11 4 2 113 393 27 0.00079 0.00054 0.00020 0.00010 0.00554 0.01928 0.00132 3w 3ac, ad, ah–ap, ar–at, 4a –h 4j 4i 4k 4l 4o 4p 4n 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 Cylindroid with scalloped edges Cylindroid with lacunose texture Cylindroid of large size with psilate texture Sub-cylindroid psilate body partly covered by a net-like pattern Large cylindroid with scrobiculate texture Ovate with granular texture Spheroid with a sub-smooth texture Large spheroid with a sub-smooth texture Large elongated sub-spheroid with irregular texture and processes Figure Continued Mercader et al. — Phytoliths from woody plants in Mozambique 95 TA B L E 2. Continued Number 49 50 51 52 53 54 55 56 57 Morphotype Descriptors Tabular ridged Tabular scrobiculate Tabular thick contorted Tabular thick dendritic Tabular thick lacunate Tabular thick sinuate Tabular thin Tabular thin pilate Tabular trapezoid % n Figure Thin parallelepiped, orbicular to square, with surface covered by ridges Variably wide parallelepiped with an elongate outline and scrobiculate texture 12 71 0.00059 0.00348 4u, v 4q– t Thick parallelepiped with a contorted profile and irregular to laminate texture 39 0.00191 3x, y, 6a, b Large elongate parallelepiped with psilate texture and sides covered by irregular dedritic processes Large thick parallelepiped with scrobiculate/lacunose texture 229 0.01124 6f, h 59 0.00289 6g, k– m Thick parallelepiped/sub-cylindroid with psilate texture. One or two sides are sinuate; sometimes, one side is sinuate and the other one is columellate Thin parallelepiped, square to rectangular shape with psilate texture Thin parallelepiped, scrobiculate or lacunate texture and rod-like processes Elongate body with a trapezoidal to triangular cross-section and psilate texture 157 0.00770 6d, e 102 8 247 0.00500 0.00039 0.01212 6c 6i 6j TA B L E 3. Rank of ash and silica producers among the species studied according to plant part, species and order Order Fabales Fabales Fabales Rosales Fabales Rosales Malpighiales Arecales Asterales Ericales Fabales Fabales Fabales Arecales Asterales Malvales Rosales Arecales Asterales Magnoliales Fabales Gentianales Malpighiales Ericales Myrtales Fabales Fabales Malpighiales Lamiales Solanales Malpighiales Fabales Gentianales Magnoliales Sapindales Malpighiales Asterales Cucurbitales Fabales Lamiales Caryophyllales Malpighiales Fabales Species Albizia anthelmintica Lonchocarpus capassa Dolichos kilimandscharicus Ficus spp. Lonchocarpus capassa Parinari spp. Pseudolachnostylis maprouneifolia Hyphaene spp. Aspilia mosambicensis Euclea crispa Albizia anthelmintica Sphenostylis spp. Piliostigma thonningii Phoenix reclinata Brachylaena spp. Monotes spp. Pouzolzia mixta Borassus aethiopum Brachylaena spp. Annona senegalensis Afzelia quanzensis Ectadiopsis oblongifolia Uapaca kirkiana Diospyros spp. Terminalia sericea Pterocarpus angolensis Sphenostylis spp. Uapaca sansibarica Kigelia africana Solanum panduriforme Uapaca nitida Cajanus cajan Vangueria infausta Xylopia aethiopica Sclerocarya birrea Antidesma spp. Pleiotaxis spp. Cucumis spp. Dolichos kilimandscharicus Lepidagathis andersoniana Celosia spp. Hymenocardia acida Acacia karoo Dry weight (g) Ash (g) Ash (%) Post-acid (g) AIF (g) Ash– AIF ( %) Dry weight– AIF ( %) Leaf Leaf Leaf Leaf Stem Leaf Leaf 2.400 5.500 1.000 2.900 14.500 1.000 1.200 0.640 1.888 0.202 0.550 3.942 0.111 0.376 26.667 34.327 20.200 18.966 27.186 11.100 31.333 0.526 1.181 0.139 0.347 1.502 0.086 0.092 0.523 1.104 0.136 0.332 1.497 0.085 0.092 81.719 58.475 67.327 60.364 37.976 76.577 24.468 21.792 20.073 13.600 11.448 10.324 8.500 7.667 1 2 3 4 5 6 7 Leaf Leaf Leaf Stem Leaf Leaf Leaf Stem Leaf Leaf Leaf Leaf Leaf Leaf Stem Leaf Leaf Leaf Stem Stem Leaf Stem Leaf Leaf Leaf Leaf Leaf Leaf Leaf Leaf Rind Stem Leaf Leaf Stem Leaf 10.200 1.000 0.800 14.300 2.800 4.300 3.000 4.400 1.900 0.600 5.500 3.700 3.600 3.000 8.800 3.000 1.600 2.600 12.700 2.800 3.600 13.100 1.500 3.600 1.500 3.000 0.800 3.100 1.900 1.000 0.800 4.200 3.000 1.000 25.600 3.800 1.004 0.167 0.127 1.184 0.311 0.559 0.192 0.323 0.148 0.105 0.418 0.395 0.454 0.281 0.570 0.190 0.161 0.185 0.774 0.327 0.225 0.822 0.158 0.297 0.117 0.227 0.060 0.381 0.275 0.099 0.084 0.120 0.262 0.113 2.271 0.350 9.843 16.700 15.875 8.280 11.107 13.000 6.400 7.341 7.789 17.500 7.600 10.676 12.611 9.367 6.477 6.333 10.063 7.115 6.094 11.679 6.250 6.275 10.533 8.250 7.800 7.567 7.500 12.290 14.474 9.900 10.500 2.857 8.733 11.300 8.871 9.211 0.703 0.069 0.049 0.769 0.134 0.184 0.120 0.171 0.074 0.023 0.191 0.117 0.130 0.093 0.269 0.087 0.047 0.066 0.344 0.059 0.076 0.258 0.030 0.062 0.027 0.053 0.015 0.054 0.030 0.017 0.014 0.054 0.037 0.014 0.310 0.046 0.700 0.066 0.047 0.766 0.129 0.184 0.118 0.166 0.070 0.021 0.188 0.117 0.113 0.090 0.261 0.084 0.043 0.066 0.297 0.056 0.071 0.257 0.028 0.062 0.025 0.049 0.013 0.050 0.029 0.015 0.011 0.053 0.037 0.012 0.293 0.043 69.721 39.521 37.008 64.696 41.479 32.916 61.458 51.393 47.297 20.000 44.976 29.620 24.890 32.028 45.789 44.211 26.708 35.676 38.372 17.125 31.556 31.265 17.722 20.875 21.368 21.586 21.667 13.123 10.545 15.152 13.095 44.167 14.122 10.619 12.902 12.286 6.863 6.600 5.875 5.357 4.607 4.279 3.933 3.773 3.684 3.500 3.418 3.162 3.139 3.000 2.966 2.800 2.688 2.538 2.339 2.000 1.972 1.962 1.867 1.722 1.667 1.633 1.625 1.613 1.526 1.500 1.375 1.262 1.233 1.200 1.145 1.132 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Part Rank Continued 96 Mercader et al. — Phytoliths from woody plants in Mozambique TA B L E 3. Continued Order Myrtales Asterales Fabales Malpighiales Malvales Fabales Fabales Sapindales Gentianales Malvales Fabales Arecales Arecales Fabales Malpighiales Malpighiales Fabales Malpighiales Gentianales Fabales Fabales Myrtales Malpighiales Myrtales Malpighiales Rosales Malpighiales Malvales Gentianales Liliales Fabales Myrtales Gentianales Fabales Lamiales Apiales Polypodiales Pandanales Magnoliales Myrtales Malpighiales Caryophyllales Myrtales Asterales Apiales Fabales Malpighiales Ericales Malpighiales Fabales Arecales Myrtales Pinales Rosales Fabales Gentianales Fabales Fabales Fabales Malpighiales Ericales Fabales Species Combretum spp. Aspilia spp. Elephantorrhiza goetzei Phyllanthus spp. Sterculia quinqueloba Pterocarpus angolensis Pterocarpus tinctorius Kirkia acuminata Crossopteryx febrifuga Monotes spp. Albizia gummifera Hyphaene spp. Hyphaene spp. Brachystegia spp. Hymenocardia acida Uapaca nitida Dalbergiella nyasae Uapaca sansibarica Strychnos spinosa Acacia tortilis Acacia schweinfurthii Syzygium guineense Pseudolachnostylis maprouneifolia Combretum imberbe Phyllanthus polyanthus Parinari spp. Phyllanthus spp. Sterculia quinqueloba Diplorhynchus condylocarpon Vellozia spp. Pterocarpus tinctorius Terminalia sericea Ectadiopsis oblongifolia Acacia spp. Kigelia africana Steganotaenia araliacea Cyclosorus spp. Pandanus livingstonianus Annona senegalensis Synaptolepis alternifolia Hymenocardia acida Celosia spp. Synaptolepis alternifolia Vernonia amygdalina Steganotaenia araliacea Brachystegia spp. Uapaca kirkiana Diospyros mespiliformis Phyllanthus polyanthus Aeschynomene spp. Borassus aethiopum Syzygium guineense Podocarpus falcatus Ficus spp. Mundulea sericea Crossopteryx febrifuga Securidaca longipedunculata Erythrophleum suaveolens Brachystegia spp. Flacourtia indica Euclea crispa Brachystegia boehmii Dry weight (g) Ash (g) Ash (%) Post-acid (g) AIF (g) Ash–AIF ( %) Leaf Leaf Leaf Leaf Leaf Leaf Leaf Leaf Stem Stem Leaf Stem Stem Stem Leaf Stem Stem Stem Leaf Leaf Leaf Leaf Stem 2.600 3.200 1.200 0.100 2.800 1.800 4.800 3.300 22.300 14.600 2.400 12.900 5.300 1.100 5.400 3.400 14.100 2.500 1.000 0.700 1.400 2.800 12.600 0.159 0.311 0.106 0.014 0.203 0.135 0.422 0.255 0.782 0.234 0.112 0.163 0.304 0.063 0.377 0.135 0.901 0.107 0.116 0.026 0.063 0.106 0.417 6.115 9.719 8.833 14.000 7.250 7.500 8.792 7.727 3.507 1.603 4.667 1.264 5.736 5.727 6.981 3.971 6.390 4.280 11.600 3.714 4.500 3.786 3.310 0.028 0.035 0.014 0.001 0.029 0.019 0.042 0.027 0.180 0.111 0.019 0.086 0.035 0.009 0.036 0.027 0.090 0.016 0.007 0.004 0.009 0.017 0.065 0.028 0.033 0.012 0.001 0.027 0.016 0.038 0.026 0.173 0.110 0.016 0.083 0.034 0.007 0.034 0.021 0.085 0.015 0.006 0.004 0.008 0.015 0.059 17.610 10.611 11.321 7.143 13.300 11.852 9.005 10.196 22.123 47.009 14.286 50.920 11.184 11.111 9.019 15.556 9.434 14.019 5.172 15.385 12.698 14.151 14.149 1.077 1.031 1.000 1.000 0.964 0.889 0.792 0.788 0.776 0.753 0.667 0.643 0.642 0.636 0.630 0.618 0.603 0.600 0.600 0.571 0.571 0.536 0.468 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 Leaf Stem Stem Stem Stem Leaf 1.400 7.100 5.000 6.000 1.500 3.200 0.091 0.201 0.138 0.362 0.124 0.163 6.500 2.831 2.760 6.033 8.267 5.094 0.008 0.031 0.023 0.028 0.009 0.012 0.006 0.029 0.020 0.024 0.006 0.012 6.593 14.428 14.493 6.630 4.839 7.362 0.429 0.408 0.400 0.400 0.400 0.375 67 68 69 70 71 72 Stem Stem Stem Leaf Leaf Leaf Leaf Stem Leaf Stem Stem Stem Stem Leaf Leaf Stem Leaf Stem Stem Leaf Leaf Stem Stem Stem Stem Leaf Leaf Stem 10.800 9.600 9.700 0.300 0.300 4.200 2.300 0.400 0.400 12.400 0.500 0.500 2.500 1.500 0.500 2.000 2.800 5.200 6.000 0.600 0.600 5.400 14.300 0.700 7.500 0.800 0.800 1.000 0.155 0.646 0.554 0.016 0.025 0.328 0.253 0.028 0.060 1.009 0.017 0.031 0.170 0.140 0.055 0.291 0.144 0.214 0.205 0.023 0.041 0.279 0.622 0.170 0.476 0.021 0.045 0.042 1.435 6.729 5.711 5.333 8.333 7.810 11.000 7.000 15.000 8.137 3.400 6.200 6.800 9.333 11.000 14.550 5.143 4.115 3.417 3.833 6.833 5.167 4.350 24.286 6.347 2.625 5.625 4.200 0.043 0.036 0.035 0.001 0.001 0.012 0.008 0.005 0.005 0.037 0.001 0.001 0.007 0.004 0.004 0.005 0.008 0.009 0.011 0.001 0.002 0.013 0.031 0.001 0.014 0.001 0.005 0.001 0.040 0.035 0.033 0.001 0.001 0.011 0.006 0.001 0.001 0.026 0.001 0.001 0.005 0.003 0.001 0.004 0.005 0.009 0.010 0.001 0.001 0.009 0.022 0.001 0.010 0.001 0.001 0.001 25.806 5.418 5.957 6.250 4.000 3.354 2.372 3.571 1.667 2.577 5.882 3.226 2.941 2.143 1.818 1.375 3.472 4.206 4.878 4.348 2.439 3.226 3.537 0.588 2.101 4.762 2.222 2.381 0.370 0.365 0.340 0.333 0.333 0.262 0.261 0.250 0.250 0.210 0.200 0.200 0.200 0.200 0.200 0.200 0.179 0.173 0.167 0.167 0.167 0.167 0.154 0.143 0.133 0.125 0.125 0.100 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 Leaf Leaf Leaf Stem Stem 1.100 1.100 1.200 1.200 1.200 0.035 0.077 0.076 0.082 0.087 3.182 7.000 6.333 6.833 7.250 0.002 0.002 0.001 0.005 0.001 0.001 0.001 0.001 0.001 0.001 2.857 1.299 1.316 1.220 1.149 0.091 0.091 0.083 0.083 0.083 101 102 103 104 105 Part Dry weight– AIF ( %) Rank Continued Mercader et al. — Phytoliths from woody plants in Mozambique 97 TA B L E 3. Continued Order Fabales Rosales Fabales Malpighiales Fabales Magnoliales Fabales Ericales Pinales Fabales Laurales Ericales Fabales Rosales Fabales Gentianales Lamiales Malvales Malpighiales Rosales Fabales Fabales Fabales Fabales Asterales Fabales Lamiales Asterales Ericales Lamiales Solanales Fabales Malpighiales Sapindales Proteales Malpighiales Malvales Proteales Ericales Gentianales Fabales Rosales Gentianales Myrtales Myrtales Gentianales Malpighiales Fabales Fabales Malvales Fabales Species Part Dry weight (g) Ash (g) Ash (%) Post-acid (g) AIF (g) Ash– AIF ( %) Pericopsis angolensis Ensete ventricosum Cajanus cajan Uapaca kirkiana Mundulea sericea Xylopia aethiopica Faidherbia albida Embelia schimperi Podocarpus falcatus Elephantorrhiza goetzei Cassytha spp. Embelia schimperi Cassia spp. Pouzolzia mixta Pterocarpus angolensis Diplorhynchus condylocarpon Vitex spp. Adansonia digitata Psorospermum febrifugum Ficus spp. Cassia spp. Acacia spp. Delonix regia Securidaca longipedunculata Pleiotaxis spp. Pericopsis angolensis Vitex spp. Vernonia amygdalina Diospyros mespiliformis Lepidagathis andersoniana Solanum panduriforme Faidherbia albida Antidesma spp. Kirkia acuminata Protea angolensis Flacourtia indica Adansonia digitata Protea angolensis Diospyros spp. Strychnos spinosa Piliostigma thonningii Ziziphus mucronata Vangueria infausta Combretum imberbe Combretum spp. Pavetta crassipes Psorospermum febrifugum Afzelia quanzensis Albizia gummifera Adansonia digitata Afzelia quanzensis Stem Stem Stem Nutshell Stem Stem Leaf Leaf Leaf Stem Stem Stem Stem Stem Inflorescence Stem 13.800 1.300 1.300 1.400 1.500 12.400 1.600 1.600 1.600 5.000 1.700 1.700 1.800 1.800 5.500 11.100 0.379 0.033 0.039 0.035 0.017 0.231 0.070 0.156 0.228 0.221 0.059 0.067 0.092 0.103 0.253 0.546 2.746 2.538 3.000 2.500 1.133 1.863 4.375 9.750 14.250 4.420 3.471 3.941 5.111 5.722 4.600 4.919 0.014 0.002 0.005 0.005 0.001 0.005 0.001 0.001 0.002 0.003 0.003 0.001 0.005 0.003 0.004 0.006 0.011 0.001 0.001 0.001 0.001 0.008 0.001 0.001 0.001 0.003 0.001 0.001 0.001 0.001 0.003 0.006 2.902 3.030 2.564 2.857 5.882 3.463 1.429 0.641 0.439 1.357 1.695 1.493 1.087 0.971 1.186 1.099 0.080 0.077 0.077 0.071 0.067 0.065 0.063 0.063 0.063 0.060 0.059 0.059 0.056 0.056 0.055 0.054 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 3.700 2.000 2.200 2.200 2.300 2.300 2.400 2.400 0.296 0.172 0.080 0.224 0.157 0.206 0.130 0.200 8.000 8.600 3.636 10.182 6.826 8.957 5.417 8.333 0.005 0.001 0.005 0.002 0.002 0.001 0.001 0.005 0.002 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.676 0.581 1.250 0.446 0.637 0.485 0.769 0.500 0.054 0.050 0.045 0.045 0.043 0.043 0.042 0.042 122 123 124 125 126 127 128 129 2.500 2.500 10.200 2.600 2.800 3.700 3.900 4.300 4.500 4.800 5.100 5.300 7.200 7.700 17.200 9.900 10.500 11.200 11.900 11.900 11.900 12.100 12.800 13.000 14.600 14.900 19.000 0.097 0.119 0.563 0.166 0.099 0.075 1.890 0.251 0.219 0.224 0.070 0.208 1.180 0.184 0.408 0.260 1.118 0.292 0.271 0.556 0.556 0.674 0.199 0.422 0.355 0.452 0.732 3.880 4.760 5.520 6.385 3.536 2.027 48.462 5.837 4.867 4.667 1.373 3.925 16.389 2.390 2.372 2.626 10.648 2.607 2.277 4.672 4.672 5.570 1.555 3.246 2.432 3.034 3.853 0.002 0.002 0.005 0.001 0.001 0.019 0.001 0.001 0.003 0.005 0.005 0.002 0.001 0.009 0.010 0.001 0.001 0.006 0.003 0.001 0.005 0.025 0.002 0.005 0.005 0.003 0.002 0.001 0.001 0.004 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 1.031 0.840 0.710 0.602 1.010 1.333 0.053 0.398 0.457 0.446 1.429 0.481 0.085 0.543 0.490 0.385 0.089 0.342 0.369 0.180 0.180 0.148 0.503 0.237 0.282 0.221 0.137 0.040 0.040 0.039 0.038 0.036 0.027 0.026 0.023 0.022 0.021 0.020 0.019 0.014 0.013 0.012 0.010 0.010 0.009 0.008 0.008 0.008 0.008 0.008 0.008 0.007 0.007 0.005 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 Leaf Leaf Leaf Stem Leaf Case Case Leaf Stem Leaf Stem Stem Leaf Stem Stem Stem Stem Stem Stem Stem Stem Leaf Stem Exocarp Stem Stem Stem Stem Stem Stem Stem Stem Stem Exocarp Case were cleaned by immersion in 5 % lab grade soap solution (Micro-90) and sonication (Fisher Scientific, FS 60) for 30 min. In situations where samples were dirt-coated the specimen was soaked in a 5 % soap –sodium hexametaphosphate water-based solution overnight in order to defloculate contaminants, followed by successive 30 min sonication cycles. Specimens were then dried at .100 8C overnight. After cooling, mass was measured on a high precision balance. The samples then went into a muffle furnace for combustion over the course of 36 h at 500 8C. The mass of the resulting ash Dry weight– AIF ( %) Rank was noted, and it then received a 10 ml 50: 50 solution made of hydrochloric and nitric acids at 3 N and was boiled. Successive washing cycles removed acids from the sample by (5 min) centrifugation at 3000 r.p.m. When acid elimination was complete, and the remainder of a sample had been dried and weighed, phosphate and carbonate loss was estimated by calculating mass differential. After this, approx. 10 ml of hydrogen peroxide at 30 % was added to the sample to destroy organic matter (if the matrix is rich in carbonates, sodium hypochlorite at 6 % is used instead; Mikutta et al., 2005). The sample was 98 Mercader et al. — Phytoliths from woody plants in Mozambique TA B L E 4. Phytolith polymorphism rates among local families Family Acanthaceae Amaranthaceae Anacardiaceae Annonaceae Apiaceae Apocynaceae Arecaceae Asteraceae Bignoniaceae Bombacaceae Bryophyte Chrysobalanaceae Clusiaceae Combretaceae Coniferophyta Cucurbitaceae Dipterocarpaceae Ebenaceae Euphorbiaceae Fabaceae Flacourtiaceae Kirkiaceae Lauraceae Moraceae Musaceae Myrsinaceae Myrtaceae Pandanaceae Podocarpaceae Polygalaceae Proteaceae Rhamnaceae Rubiaceae Solanaceae Sterculiaceae Tamaricaceae Thelypteridaceae Thymelaceae Urticaceae Velloziae Verbenaceae Species (n) Morphotype (n) 1 1 1 2 1 3 3 5 1 1 1 1 1 3 1 1 1 3 8 28 1 1 1 2 1 1 1 1 1 1 1 1 3 1 1 1 1 1 1 1 1 20 13 6 15 5 12 16 23 6 16 1 10 12 18 11 4 10 10 23 35 5 3 0 7 1 15 8 3 7 6 15 5 25 12 11 5 1 4 3 7 4 dried at .100 8C overnight. The resulting biominerals formed the acid-insoluble fraction (AIF) and it was here where phytoliths, among other biogenic precipitates, were found. An aliquot of 0.001 g was taken for mounting, after proper mixing of this extract by vortexing. The mounting medium was made up of two droplets of resin solution ‘Entellan New’. The aliquot was well mixed, and the microscopic inspection and counting took place within 48 h of mounting before media were able to dry (3-D shifting of phytoliths was necessary to carry out identification: system microscope, Olympus BX51; 400 magnifications). Inspection and counting were done under polarized light, regular light microscopy and differential interference contrast (DIC) which greatly enhances contrast and resolves fine structural details. In total, 180 discrete samples representing .41 families, .77 genera and . 90 species of vascular plants have been analysed. Two bryophytes were also included. Stem (n ¼ 78) and leaf (n ¼ 78) tissue were processed separately. Inflorescences, exocarps, nutshells, legume cases and seeds were also processed. The total number of phytoliths counted is 20 372. Average count per species, all tissues combined, is 216. Specimens that yielded very little silica were scanned at least ten times (the coverslip measures 22 mm in length) in adjacent but not overlapping lines. The percentage of each morphotype per species was calculated (Table 2), and types are described according to the descriptors from the International Code for Phytolith Nomenclature 1.0 (Madella et al., 2005). Phytoliths were grouped into 57 morphotypes (two were articulated forms and 55 were discrete shapes) (Table 2). Once quantified (Albert et al., 1999, 2003; Tsartsidou et al., 2007), the phytoliths were subjected to statistical analyses. Cluster analysis (CA) and principal component analysis (PCA) were employed to reduce the large number of variables in the collection to a smaller set of principal components, reveal internal structure, group type variables and detect covariance (Kim and Mueller, 1978; Basilevsky, 1994; Jollife, 2002). We did not normalize the data for the PCA and ran it on the original correlation matrix. For the CA, we used Ward’s method and the squared Euclidean distance with the variables rescaled to 0 – 1. PCA and CA had matching results. Due to this triangulation, we decided against conducting additional robustness tests. Discriminant analysis (DA) has long been used to identify variables that may classify unknown specimens into known categories because of its ability to detect group-indicators (or predictor phytoliths) and quantify the score on which such grouping variables indicate membership of a given group (Huberty, 1994). Beginning with Fisher’s (1936) pioneering work, such studies have proven useful in plant classification (e.g. Ball et al., 1999; Lu and Liu, 2005). For the present study, the quantified phytolith morphotype data were subjected to a series of exploratory DAs using the SYSTATw 10 software package (SPSS Inc. 2000) that were aimed at identifying morphotype associations that might identify appropriate groups accurately. The large number of null values was problematic and action had to be taken to reduce their numbers, and therefore all cases with fewer than 50 phytoliths and unique morphotypes (see below) were excluded. Exploratory data analysis revealed strong differences in both phytolith quantity and morphotype presence between stem and leaf tissues from the same taxon. It was reasoned that combining morphotype samples from stem and leaf tissues would tend to obscure possible patterning in taxon-specific morphotype associations, and the data set was split into two groups containing phytoliths from either stem or leaf tissue only. R E S U LT S Biomineral production In Table 3 we present the reader with AIF percentages expressed in two separate columns as functions of both the plant’s dry weight and its ash. Note that the plant’s dry weight contains an arbitrary content of volatile organic components, which disappears by reduction of the sample to ashes. Ash and biomineral contents are expressed in Table 3. Silica production averages 1.42% of the plant’s dry weight (range: 0.005–21.79 %). We provide a silica-accumulator rank as well, in which higher units denote greater silica production. The mean content of biogenic silica per ash sample is 13.52 %. Leaf tissue produces an average of 18.60 % AIF (range: 0.43–81.71 %), while stems Mercader et al. — Phytoliths from woody plants in Mozambique 99 35 µm 230 µm F I G . 2. (a) Cylindroid, Fabaceae, Dichrostachys cinerea. Leaf. (b) Cylindroid bulbous, Polygalaceae, Securidaca longipedunculata. Stem. (c) Cylindroid bulbous, Proteaceae, Protea angolensis. Leaf. (d) Cylindroid crenate, Ebenaceae, Euclea crispa. Stem. (e) Cylindroid lacunate, Clusiaceae, Psorospermum febrifugum. Stem. (f ) Cylindroid reticulate, Solanaceae, Solanum panduriforme. Leaf. (g) Cylindroid scrobiculate, Myrsinaceae, Embelia schimperi. Leaf. (h) Epidermal jig-saw, Fabaceae, Albizia anthelmintica. Leaf. (i) Epidermal jig-saw, Fabaceae, Afzelia quanzensis. Leaf. ( j) Cylindroid large, Verbenaceae, Vitex spp. Stem. (k) Epidermal polygonal, Arecaceae, Hyphaene spp. Leaf. (l) Epidermal polygonal, Fabaceae, Lonchocarpus capassa. Leaf. (m) Epidermal polygonal, Anacardiaceae, Sclerocarya birrea. Leaf. (n) Epidermal polygonal, Moraceae, Ficus spp. Leaf. (o) Epidermal polygonal, Euphorbiaceae, Antidesma spp. Leaf. ( p) Cylindroid columellate, Apocynaceae, Ectadiopsis oblongifolia. Stem. (q) Epidermal polygonal, Euphorbiaceae, Uapaca kirkiana. Leaf. (r) Cylindroid columellate, Fabaceae, Albizia anthelmintica. Stem generate a mean AIF of 9.52 % (range: 0.053–64–69 %). High biomineral content (i.e. twice the average) in leaves has been recorded among members of the Malphigiales, Malvales, Arecales, Rosales and Fabales, while stem biominerals peak among the Gentianales, Liliales, Lamiales, Malvales, Arecales, Asterales and Fabales. The Fabales display the widest production range and plot throughout the spectrum. Yet, it is worth noting that four members are among the top ten producers, above wellknown silica accumulators such as the Arecales, Asterales and, to a lesser extent, the Ericales. From a morphotype diversity point of view, the average number of morphotypes produced by a given family (Table 4) is 11 (range: 1 – 35), 21 families created 10 types, 12 families generate between 11 and 20 morphotypes, and only four yielded .20 types (Fabaceae, 35; Rubiaceae, 25; Asteraceae/Euphorbiaceae, 23). Within the Fabaceae, at the subfamily level, the morphotype variability rank is highest among the Caesalpiniodeae (seven species, 30 types) followed by the Papilionoideae (eight species, 23 types), the Mimosoideae (.10 species, 15 types) and the Faboideae (two species, 15 types). Description of common morphotypes Eighty-five per cent of the variability documented here is accounted for by a sub-set of phytoliths comprising ten morphotypes. In order of frequency these are as follows. Epidermal polygonal (morphotype 22, n ¼ 4945, approx. 24 % of the total assemblage, Fig. 2k – n, q). This morphotype represents leaf epidermal tissue in which the cell shape is isodiametric; it is very abundant (mean value per species is 36 % of the phytoliths produced; range: 1 – 100 %). A total of five families are above-average producers (at least twice more than average) including the Anacardiaceae, Euphorbiaceae, Fabaceae, Moraceae and the Verbenaceae. Among these top producers, the maximum length of the cell ranges from 18 to 33 mm. Their cell wall thickness varies from 1 mm (Lonchocarpus capassa, Pseudolachnostylis maprouneifolia) to 1.8 mm 100 Mercader et al. — Phytoliths from woody plants in Mozambique 20 µm 40 µm F I G . 3. (a) Vessel member, Combretaceae, Combretum imberbe. Leaf. (b) Epidermal laminate, Fabaceae, Cassia spp. Leaf. (c) Globular echinate, Arecaceae, Hyphaene spp. Mature stem. (d) Globular echinate large, Arecaceae, Hyphaene spp. Mature stem. (e) Globular scrobiculate, Cucurbitaceae, Cucumis spp. Rind. (f ) Globular scrobiculate, Podocarpaceae, Podocarpus falcatus. Leaf. (g) Globular facetate, Thymelaceae, Synaptolepis alternifolia. Leaf. (h) Globular facetate, Cucurbitaceae, Cucumis spp. Rind. Side view. (i) Globular folded, Fabaceae, Afzelia quanzensis. Leaf. ( j) Globular folded, unknown, Rorola. Leaf. (k) Globular folded, Bombacaceae, Adansonia digitata. Exocarp. (l) Globular folded, Apocynaceae, Diplorhynchus condylocarpon. Leaf. (m) Globular folded, Bombacaceae, Adansonia digitata. Exocarp. (n) Globular folded, Bombacaceae, Adansonia digitata. Exocarp. (o) Globular granulate, Fabaceae, Pterocarpus angolensis. Stem. ( p) Globular psilate, Fabaceae, Brachystegia boehmii. Stem. (q) Globular granulate large, Fabaceae, Elephantorrhiza goetzei. Leaf. (r) Globular tuberculate, Urticaceae, Pouzolzia mixta. Leaf. (s) Globular tuberculate, Fabaceae, Acacia spp. Stem and leaf. (t) Globular granulate oblong, Unknown, Mchele. Leaf. (u) Globular psilate, Proteaceae, Protea angolensis. Leaf. (v) Globular psilate large, Euphorbiaceae, Uapaca sansibarica. Stem. (w) Spooliform, Proteaceae, Protea angolensis. Leaf. Abaxial and side views. (x) Tabular thick contorted (laminate variant), Fabaceae, Acacia tortilis. Leaf. (y) Tabular thick contorted (laminate variant), Fabaceae, Acacia tortilis. Leaf. (z) Globulose, Fabaceae, Brachystegia spp. Stem. (aa) Globulose, Fabaceae, Brachystegia spp. Stem. (ab) Lenticular concave/convexe, Amaranthaceae, Celosia spp. Leaf. (ac) Hair base, Euphorbiaceae, Hymenocardia acida. Leaf. (ad) Hair, Fabaceae, Cajanus cajan. Leaf. (ae) Globulose bisected, Solanaceae, Solanum panduriforme. Leaf. Abaxial and side views. (af ) Shield, Solanaceae, Solanum panduriforme. Leaf. (ag) Shield, Sterculiaceae, Sterculia quinqueloba. Leaf. (ah) Hair, Urticaceae, Pouzolzia mixta. Leaf. (ai) Hair, Asteraceae, Aspilia mosambicensis. Leaf. (aj) Hair, Fabaceae, Albizia anthelmintica. Leaf. (ak) Hair base, Fabaceae, Albizia anthelmintica. Leaf. Side view. (al) Hair base, Fabaceae, Lonchocarpus capassa. Leaf. Side view. (am) Hair base, Fabaceae, Mngwemba. Leaf. (an) Hair base, Thymelaceae, Synaptolepis alternifolia. Leaf. Abaxial and side views. (ao) Hair base, Unknown, Chipiongule. Abaxial and side views. (ap) Hair base, Fabaceae, Acacia spp. (aq) Tabular thick dendritic, Arecacae, Hyphaene spp. Mature stem. (ar) Hair base, Asteraceae, Pleiotaxis spp. Leaf. (as) Hair base, Combretaceae, Combretum imberbe. Leaf. Side view. (at) Hair, Amaranthaceae, Celosia spp. Leaf. (Sclerocarya birrea) and 3.7 mm (Uapaca kirkiana) The cell surface can be psilate, granulate or reticulate. The richest producer of this type is Phyllanthus spp. (Euphorbiaceae), in which 100 % of the phytoliths found belong to this category. Stomata/hair/base (morphotype 41, n ¼ 3454, approx. 17 % of the total assemblage, Fig. 3ad, ah –at; 4a– h). This comprises the leaf stomatal complex, trichome bases and hairs. This morphotype reaches a mean frequency of 25 % of the types produced by a given species (range: 1 – 82 %). A very diverse group of unrelated families produce it in numbers that exceed twice the average, including the Asteraceae, some bryophytes, the Ebenaceae, Euphorbiaceae, Fabaceae and the Urticaceae. The highest value is documented in Pouzolzia mixta, of the Urticaceae, in which 82 % of the phytoliths produced by the species belong to this group. The long trichome is slender and measures between 50 and .100 mm (e.g. Fabaceae and Urticaceae), while the small type is short and thick with a maximum length ,50 mm. Both types can be psilate or papilate (e.g. Aspilia mosambicensis) and the two types may appear in the same specimen. Some species do possess hairs with both very square and acute tips (e.g. Albizia anthelmintica). Vessel members (morphotype 23, n ¼ 2133, approx. 10 % of the total assemblage, Fig. 3a, b). This morphotype derives from the xylem’s tracheary elements. The average frequency per species is 19 % (range: 1 – 91 %). Four families produce numbers twice as high as the average, and these are the Clusiaceae, Apocynaceae, Combretaceae and the Fabaceae. Importantly, the Fabaceae is the topmost producer, with values .50 % in Mundulea sericea (91 %). Mercader et al. — Phytoliths from woody plants in Mozambique 101 F I G . 3. Continued. Globular psilate (morphotype 31, n ¼ 1924, 9.5 % of the total assemblage, Fig. 3p). Mean production reaches 20 % per species (range: 1–100 %). A total of six families can be considered very high producers of globular psilates and they include the Arecaceae, Chrysobalanaceae, Euphorbiaceae, Fabaceae, Kirkiaceae and Proteaceae. The highest abundance is seen in Kirkia acuminata (Kirkiaceae: 100 %). Size is bimodal, but the mean maximum length always is ,10 mm. Protea angolensis produces globular psilates that measure 3.4 + 0.73 mm (n ¼ 107). The mean size of these globular types in Pericopsis angolensis is 5.1 + 1.7 mm (n ¼ 200), while it increases to 7.8 + 2.4 mm (n ¼ 171) for Kirkia acuminata and to 8.5 + 3 mm (n ¼ 200) in Parinari spp. This morphotype may occur indiscriminately in both stem and leaf tissue of the same species (e.g. in the Fabaceae); however, there are families in which globular psilate shapes are exclusive to the leaf (Apocynaceae, Bignoniaceae, Clusiaceae, Myrsinaceae, Myrtaceae, Pandanaceae, Podocarpaceae, Proteaceae, Solanaceae, Sterculiaceae and Verbenaceae) or the stem (Annonaceae, Arecaceae, Bombacaceae, Chrysobalanaceae, Dipterocarpaceae, Euphorbiaceae, Flacourtiaceae, Kirkiaceae, Polygalaceae and Rubiaceae). Globular granulate (morphotype 28, n ¼ 1616, approx. 8 % of the total assemblage, Fig. 3o). The average quantity per species is 20 % of the total (range: 1 – 100 %). Top producers are members of the Cucurbitaceae, Fabaceae, Annonaceae, Apocynaceae and the Musaceae. The highest rates have been documented among the Apocynaceae and Musaceae, in which this morphotype represents most or all of the phytoliths present. In these cases, the size ranges from an average of 12 mm (e.g. Musaceae) to 20 mm (e.g. Apocynaceae, Annonaceae). Sometimes globular granulates appear in both stem and leaf tissue. Yet, in general, this morphotype reaches higher absolute and relative frequencies in stem tissue compared with other plant parts such as leaf, exocarp and inflorescence. In five families the globular granulate is restricted to leaf tissue: Apiaceae, Arecaceae, Bignoniaceae, Myrsinaceae and Solanaceae. Among the Fabaceae, we note that this type is often present, but generally in low proportions (,14 % of the total per species, range: 2 – 53 %). In fact, we rarely see any species with truly high production rates (exception: Dalbergiella nyasae). Globular echinate (morphotype 24, n ¼ 677, approx 3 % of the total assemblage, Fig. 3c). This is is produced exclusively by the Arecaceae. The average percentage in a given species is 33 (range: 11– 64 %). This phytolith is produced in stem, leaf and inflorescence tissues. The highest yield observed by us is by Hyphaene spp. Size varies across species, from about 7 mm for Borassus aethiopum to 14 mm for Hyphaene spp. Blocky polygonal (morphotype 7, n ¼ 668, approx. 3 % of the total assemblage, Fig. 5t). This type is a body with a psilate to ridged texture that may appear articulated or individually. Its size ranges from 25 to .50 mm. Few families produce this morphotype in a significant proportion; namely, the Apocynaceae (Ectadiopsis oblongifolia), Asteraceae (Brachylaena spp.) and Fabaceae (Albizia anthelmintica). For the most part, this morphotype is generated in stems. Epidermal jig-saw (morphotype 20, n ¼ 651, approx. 3 % of the total assemblage, Fig. 2h, i, o). This type represents leaf epider- mal tissue in which the cell shape is irregular. Mean frequency 102 Mercader et al. — Phytoliths from woody plants in Mozambique 65 µm F I G . 4. (a) Hair, Asteraceae, Pleiotaxis spp. Leaf. (b) Hair base, Asteraceae, Aspilia spp. Leaf. (c) Hair base, Ebenaceae, Diospyros spp. Leaf. (d) Hair base, Fabaceae, Albizia anthelmintica. Leaf. Side view. (e) Hair base, Fabaceae, Albizia anthelmintica. Leaf. Abaxial view. (f ) Hair base, Fabaceae, Afzelia quanzensis. Leaf. (g) Hair, Bryophyte, Changula. Leaf. (h) Stomata cell, Arecacae, Borassus aethiopum. Leaf. (i) Tabular crenate, Lauraceae, Cassytha spp. Leaf. ( j) Tabular corniculate, Combretaceae, Combretum spp. Leaf. (k) Tabular elongate, Acanthaceae, Lepidagathis andersoniana. Stem. (l) Tabular facetate, Bryophyte, Changula. Leaf. (m) Tabular oblong, Euphorbiaceae, Uapaca sansibarica. (n) Tabular psilate, Asteraceae, Aspilia spp. Leaf. (o) Tabular lanceolate, Euphorbiaceae, Uapaca kirkiana. Leaf. (p) Tabular oblong, Euphorbiaceae, Uapaca kirkiana. Stem. (q) Tabular scrobiculate, Fabaceae, Lonchocarpus capassa. Stem, (r) Tabular scrobiculate, Solanaceae, Solanum panduriforme. Leaf. (s) Tabular scrobiculate, Fabaceae, Acacia karoo. Stem and leaf. (t) Tabular scrobiculate, Euphorbiaceae, Uapaca nitida. Stem. (u) Tabular ridged, Ebenaceae, Euclea crispa. Leaf. (v) Tabular ridged, Bignoniaceae, Kigelia africana. is 22 % of the phytoliths produced by a given species (range: 1 – 74 %). Only one family is a high producer (twice or more than average), the Thelypteridaceae; although four families produce just above average: Euphorbiaceae, Asteraceae, Combretaceae and Fabaceae (in Afzelia quanzensis this morphotype represents 40 % of the total assemblage produced by the species). Among these top producers, the maximum length of the cell ranges from 28 to 65 mm. Their cell wall Mercader et al. — Phytoliths from woody plants in Mozambique 103 40 µm 20 µm F I G . 5. (a) Blocky, Amaranthaceae, Celosia spp. Leaf. (b) Blocky, Fabaceae, Pterocarpus angolensis. Stem. (c) Blocky, Clusiaceae, Psorospermum febrifugum. Stem. (d) Blocky, Fabaceae, Pterocarpus tinctorius. Stem. (e) Blocky, Fabaceae, Pterocarpus angolensis. Stem. (f ) Blocky, Ebenaceae, Euclea crispa. Stem. (g) Blocky, Clusiaceae, Psorospermum febrifugum. Stem. (h) Blocky, Clusiaceae, Psorospermum febrifugum. Leaf. (i) Blocky, Fabaceae, Brachystegia spp. Stem. ( j) Blocky, Solanaceae, Solanum panduriforme. Leaf. (k) Blocky, Fabaceae, Piliostigma thonningii. Stem. (l) Blocky, Annonaceae, Annona senegalensis. Stem. (m) Blocky, Amaranthaceae, Celosia spp. Leaf. (n) Blocky, Rubiaceae, Pavetta crassipes. Stem. (o) Blocky cavate, Bignoniaceae, Kigelia africana. Stem. ( p) Blocky corniculate, Cucurbitaceae, Cucumis spp. Rind. (q) Blocky facetate, Euphorbiaceae, Uapaca nitida. Stem. (r) Blocky hairy, Podocarpaceae, Podocarpus falcatus. Leaf. (s) Blocky pilate, Euphorbiaceae, Uapaca nitida. Stem. (t) Blocky polygonal, Apocynaceae, Ectadiopsis oblongifolia. Stem. (u) Blocky radiating, Fabaceae, Aeschynomene spp. Leaf. (v) Blocky trapezoid, Coniferophyta, Likualambuti. Leaf. (w) Blocky tuberculate, Solanaceae, Solanum panduriforme. Leaf. (x) Clavate granulate, Dipterocarpaceae, Monotes spp. Stem. thickness is around 1.2 mm. The cell wall in some species is pitted (e.g. Afzelia quanzensis). The cell surface is mostly psilate, but some specimens display sulcate textures (e.g. Cyclosorus spp.). Cylindroid bulbous (morphotype 13, n ¼ 616, approx. 3 % of the total assemblage, Fig. 2b, c). The mean frequency of this type is 9 % (range: 1 – 73 %). Only two families produce this type at a level twice the average, and these are the Fabaceae (Piliostigma thonningii and Pterocarpus angolensis) and the Arecaceae (Phoenix reclinata). This type appears in small and medium sizes, but in some instances it can be .50 mm long, even .100 mm. Blocky (morphotype 1, n ¼ 483, 2.5 % of the total assemblage, Fig. 5a –n). The average representation per species is 7 % (range: 1–29 %). Five families produce twice the average: Acanthaceae, Rhamnaceae, Fabaceae, Asteraceae and Rubiaceae. The highest production rate (29 %) is documented in the stem of Pavetta crassipes (Rubiaceae). This type appears in stem tissue twice as frequently as it is documented in leaf, exocarp or the legume case. Only rarely are blocky shapes 104 Mercader et al. — Phytoliths from woody plants in Mozambique 100 µm F I G . 6. (a) Tabular thick contorted, Fabaceae, Acacia spp. Stem and leaf. (b) Tabular thick contorted, Chrysobalanaceae, Parinari spp. Leaf. (c) Tabular thin, Fabaceae, Dalbergiella nyasae. Stem. (d) Tabular thick sinuate, Fabaceae, Albizia anthelmintica. Leaf. (e) Tabular thick sinuate, Solanaceae, Solanum panduriforme. Leaf. (f) Tabular thick dendritic, Bignoniaceae, Kigelia africana. Stem. Abaxial and side views (upper and lower images, respectively). (g) Tabular thick lacunate, Apocynaceae, Ectadiopsis oblongifolia. Stem. (h) Tabular thick dendritic, Rubiaceae, Vangueria infausta. Stem. (i) Tabular thin pilate, Lauraceae, Cassytha spp. Leaf. ( j) Tabular trapezoid, Euphorbiaceae, Uapaca kirkiana. Stem. (k) Tabular thick lacunate, Asteraceae, Aspilia mosambicensis. Leaf. (l) Tabular thick lacunate, Amaranthaceae, Celosia spp. Leaf. (m) Tabular thick lacunate, Rubiaceae, Crossopteryx febrifuga. Leaf. (n) Globular verrucate oblong, Ebenaceae, Euclea crispa. Stem. found in both stem and leaf tissue of the same species (Mundulea sericea, Pterocarpus angolensis; Fabaceae/Sterculia quinqueloba, Sterculiaceae). It is exclusive to the stem tissue of the Annonaceae, Apocynaceae, Asteraceae, Amaranthaceae, Clusiaceae, Combretaceae, Euphorbiaceae, some members of the Fabaceae, Polygalaceae, Rhamnaceae, Rubiaceae and Verbenaceae. Conversely, the blocky type is exclusive to the leaf tissue of the Apiaceae, Arecaceae, Clusiaceae, Flacourtiaceae, Myrsinaceae, Podocarpaceae, Proteaceae and Solanaceae. Unique phytoliths There are seven morphotypes that are exclusive to the species level. These types are (1) blocky facetate (morphotype 4, n ¼ 1, Uapaca nitida, Fig. 5q); (2) epidermal laminate (morphotype 21, n ¼ 1, Cassia spp., Fig. 3b); (3) globulose bisected (morphotype 37 n ¼ 2, Solanum panduriforme, Fig. 3ae); (4) cylindroid reticulate (morphotype 18, n ¼ 6, Solanum panduriforme, Fig. 2f ); (5) tabular thin pilate (morphotype 56, n ¼ 8, Cassytha spp., Fig. 6i); (6) blocky hairy (morphotype 5, n ¼ 9, Podocarpus falcatus, Fig. 5r); and (7) blocky radiating (morphotype 8, n ¼ 56, Aeschynomene spp., Fig. 5u). Altogether these types represent 0.0043 % of the total assemblage, with negligible intraspecies percentages ranging from 0.002352941 to 0.185430464 %. Obviously, these idiosyncratic morphotypes have very high taxonomic value, but their low numbers make their detection in small collections exceedingly unlikely. Note that for the proportions of these unique phytoliths to reach a mere 1 % of a given assemblage the investigator would need to study a very species-rich botanical collection and carry out extremely high total phytolith counts, in the order of 75 000 – 4 000 000. Statistical classification, taxonomy and grouping Backward, stepwise DAs were run on the stem vs. leaf data set to find morphotype associations that could be useful in TA B L E 5. Discriminant analysis (DA) of the stem tissue data set: classification matrix, DA and cross-validation by SYSTAT 10 ‘Jackknife’ procedure DA. Classification matrix results Asterales 2 Caryophyllales 0 Fabales 0 Gentianales 0 Magnoliales 0 Malpighiales 0 Malvales 0 Myrtales 0 Rosales 0 Solanales 0 Totals 2 DA. Classification matrix results: jacknifed Asterales 0 Caryophyllales 0 Fabales 0 Gentianales 0 Magnoliales 0 Malpighiales 0 Malvales 0 Myrtales 0 Rosales 0 Solanales 0 Total number classified 0 Actual number 2 Caryophyllales Fabales Gentianales Magnoliales Malpighiales Malvales Myrtales Rosales Solanales % Correct 0 1 0 0 0 0 0 0 0 0 1 0 0 11 0 0 0 0 0 0 0 11 0 0 0 2 0 0 0 0 0 0 2 0 0 0 0 2 0 0 0 0 0 2 0 0 0 0 0 4 0 0 0 0 4 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 2 0 2 0 0 0 0 0 0 0 0 0 1 1 100 100 100 100 100 100 100 100 100 100 100 0 1 0 0 0 0 0 0 0 0 1 1 0 0 2 0 0 1 0 1 1 0 5 11 2 0 0 0 1 0 0 0 1 0 4 2 0 0 0 1 0 1 0 0 0 0 2 2 0 0 1 0 0 1 0 0 0 0 2 4 0 0 0 0 0 0 1 0 0 0 1 1 0 0 4 0 1 1 0 0 0 0 6 1 0 0 1 1 0 0 0 0 0 0 2 2 0 0 3 0 0 0 0 0 0 1 4 1 0 100 18 0 0 25 100 0 0 100 22 Wilks’ l ¼ 0.0000, d.f. ¼ 16, 9, 17. Approximate F ¼ 9.4353, d.f. ¼ 144 31, P , 0.0001. Morphotypes employed: 1, 7,12, 13, 16, 27, 28, 29, 30, 31, 34, 38, 41, 42, 45, 46 and 47. Mercader et al. — Phytoliths from woody plants in Mozambique Asterales 105 106 TA B L E 6. Principal component analysis (PCA) of stem morphotypes (by SPSS, 15) Cluster number Case number 1 1 28 2 2 2 2 4 11 3 3 3 3 3 5 6 8 3 9 3 12 3 3 14 16 3 17 3 20 3 21 3 22 3 23 3 26 3 3 27 29 4 5 7 10 6 6 7 8 9 10 13 25 15 18 19 24 Fabales Family Fabaceae Species Afzelia quanzensis Magnoliales Annonaceae Xylopia aethiopica Fabales Fabaceae Albizia anthelmintica Asterales Asteraceae Brachylaena spp. Gentianales Apocynaceae Ectadiopsis oblongifolia Magnoliales Annonaceae Annona senegalensis Fabales Fabaceae Brachystegia spp. Fabales Fabaceae Cajanus cajan Fabales Fabaceae Dalbergiella nyasae Gentianales Apocynaceae Diplorhynchus condylocarpon Rosales Musaceae Ensete ventricosum Lamiales Bignoniaceae Kigelia africana Malpighiales Euphorbiaceae Phyllanthus polyanthus Fabales Fabaceae Piliostigma thonningii Fabales Fabaceae Pterocarpus angolensis Fabales Polygalaceae Securidaca longipedunculata Solanales Solanaceae Solanum panduriforme Myrtales Combretaceae Terminalia sericea Malpighiales Euphorbiaceae Uapaca sansibarica Fabales Fabaceae Unknown Fabales Fabaceae Pterocarpus tinctorius Caryophyllales Amaranthaceae Celosia spp. Fabales Fabaceae Dolichos kilimandscharicus Arecales Arecaceae Hyphaene spp. Malpighiales Euphorbiaceae Uapaca nitida Malvales Dipterocarpaceae Monotes spp. Asterales Asteraceae Pleiotaxis spp. Rosales Urticaceae Pouzolzia mixta Malpighiales Euphorbiaceae Uapaca kirkiana Blocky Blocky Clavate Cylindroid polygonal tuberculate granulate columellate Cylindroid large Globular folded Globular granulate large Globular granulate oblong Globular psilate large Globular tuberculate Tabular crenate Tabular ridged Tabular scrobiculate Tabular thin 0 0 0 0 0 0 47 0 0 3 0 0 0 0 0 0 0 0 0 0 0 78 0 0 0 0 0 0 0 0 0 221 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 219 214 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 4 14 19 0 6 0 0 0 7 2 1 5 0 0 0 3 1 1 48 37 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 87 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 38 0 0 1 0 0 0 0 0 0 0 0 0 0 39 0 0 0 0 0 0 0 0 0 0 0 0 6 0 33 0 6 0 0 0 0 0 0 0 35 Mercader et al. — Phytoliths from woody plants in Mozambique 1 Order Blocky pilate 20.077 0.025 20.076 0.026 0.027 0.872 20.071 20.075 0.014 0.028 20.411 20.340 0.022 0.140 0.011 20.046 20.072 20.016 20.033 20.043 20.120 0.837 20.028 20.043 0.840 20.266 0.016 20.033 20.054 20.041 0.890 20.067 20.022 20.036 20.049 20.057 20.071 20.036 20.048 20.036 20.198 20.034 20.035 0.851 20.045 Extraction method: principal component analysis. Rotation method: Varimax with Kaiser normalization. Rotation converged in seven iterations. 20.029 20.057 20.007 20.034 20.035 20.109 20.057 20.013 20.013 20.022 20.128 20.073 0.989 20.049 0.990 Blocky pilate Blocky polygonal Blocky tuberculate Clavate granulate Cylindroid columellate Cylindroid large Globular folded Globular granulate large Globular granulate oblong Globular psilate large Globular tuberculate Tabular crenate Tabular ridged Tabular scrobiculate Tabular thin 20.047 20.044 0.988 20.057 20.011 0.047 20.001 0.984 0.092 20.023 0.100 0.192 20.026 20.006 20.003 20.026 20.058 0.027 0.988 20.037 20.119 20.059 0.018 0.988 20.021 20.119 20.095 20.020 20.054 20.027 20.034 0.902 20.021 20.040 0.897 20.181 20.091 20.033 20.051 20.029 20.211 20.159 20.037 20.075 20.050 6 5 4 2 1 3 Stem Component 7 Mercader et al. — Phytoliths from woody plants in Mozambique 107 classifying unknown morphotype samples to the order level (Table 5). These data sets contain relatively few cases per order [e.g. for the stem tissue data set, n varies between 1 and 11, with eight of the ten orders present in the sample being represented by only one (n ¼ 4) or two (n ¼ 4) cases]. These are small numbers, but, given the pioneering nature of the present study, it was felt that our results may guide future research efforts and develop a better understanding of the available data. DA of the leaf tissue sample did not result in successful identification of morphotype associations that could be used reliably to assign unknown samples to the order level. An exception to this overall result is the order Rosales, which has quite distinctive leaf tissue phytolith morphotype associations, but the failure of classification for the remaining orders and the misclassification of non-Rosales specimens as Rosales makes the production of a useful classification function problematic. It may be that further work with larger numbers of cases per order might resolve this problem but, for the present, leaf phytolith morphotype associations cannot be used to classify unknown materials. DA of the stem tissue data set, on the other hand, initially appeared to be very successful. Of the ten orders present, 100 % were correctly classified by the analysis. Using the same data both to calculate discriminant functions and then to estimate their accuracy, however, tends to overestimate the usefulness of the discriminant functions in classifying new data. Cross-validation was conducted using the SYSTATw 10 ‘Jackknife’ procedure (SPSS Inc.: I:292). Jackknifing involves computing functions using all available data except the cases being classified, i.e. as each case is classified it is excluded from the discriminant function calculation that is used to classify it. This procedure almost always produces poorer but more realistic results than using the entire data set to predict group membership on a post hoc basis. The results of the jackknifed classification procedure are much poorer than the initial run (Table 5); only 22 % of cases were correctly assigned. Nevertheless, jackknifing correctly classified three orders at 100 % (Caryophyllales, Malvales and Solanales), and two more (Fabales and Malphigiales) were correctly classified at 18– 25 %. Divergent results from the two above discriminant procedures highlight the fact that there are too many predictors (SPSS Inc.:I:292). However, the better-than-chance outcome is an indication of an underlying association pattern that, with further study, might be useful in classifying unknown samples. It is anticipated that increasing the number of specimens per order could substantially improve the robustness of the results, and would allow us to explore if there could be predictors that may be able to identify, for example, Fabaceae subfamilies (cf. Soladoye, 1982). The CA and PCA were run on the full data set to determine the consistency of the morphotype signal from different families and orders, and all types that did not load per iteration (seven iterations for the stem data) were dropped, until the data reached a simple structure in which each remaining morphotype loaded to only one component (Table 6; Fig. 7). The first two axes of the PCA account for 26.8 % of the total variance for stem, and 42.9 % for leaf tissue (not presented here). For stem data alone, we found that 15 phytolith morphotypes created seven principal components (types 6, 7, 10, 11, 14, 17, 27, 29, 30, 32, 34, 43, 49, 50 and 55). Note that the type 108 Mercader et al. — Phytoliths from woody plants in Mozambique Tabular ridged 1·0 Tabular thin Component 2 0·5 Globular psilate large Blocky tuberculate Cylindroid columellate Globular folded Blocky pilate Globular granulate oblong Clavate granulate Globular granulate large Tabular crenate Tabular scrobiculate Blocky polygonal Globular tuberculate Cylindroid large 0·0 –0·5 –0·5 0·0 0·5 1·0 Component 1 F I G . 7. Principal component analysis (PCA) ordination diagram (SPSS 15) of the stem morphotypes showing the relationship between phytolith types. ‘cylindroid scrobiculate’ was dropped because of perfect correlation with the type ‘cylindroid large’, and the latter was kept because it displayed more variance. Leaf tissue yielded six principal components ( phytolith morphotypes 7, 11, 15, 16, 19, 30, 32, 39, 43, 46, 47, 48, 50 and 57). For stem and leaf tissue combined, the identification of specific morphotypes as principal components overlaps across five morphotypes: 7, 11, 30, 32, 43 and 50. The cluster ordination of stem morphotypes relative to families and species was conducted on the basis of both linkage distance among phytolith morphotypes and their associations. The resulting dendrogram (Fig. 8) shows well-defined groups that have within themselves similar samples; also the cluster diagram by phytolith morphotype matches the PCA results closely. The number of clusters thus identified is ten (Table 6). Cluster number three separates out from the rest clearly, but the short rescaled linkage distance for all of its samples (,1) highlights the fact the (taxonomically unrelated) families contained therein have the least distinctiveness of all clusters. Contrarily, the wider dissimilarity coefficient seen in the remaining nine clusters speaks to the distinctiveness displayed by several members of the Amaranthaceae, Annonaceae, Apocynaceae, Arecaceae, Asteraceae, Dipterocarpaceae, Euphorbiaceae, Fabaceae and Urticaceae. In a separate dendrogram (not presented here) leaf morphotypes cluster similarly to stem types, and the overlap includes species from the Amaranthaceae, Annonaceae, Apocynaceae and the Asteraceae. DISCUSSION We have supplied the reader with the phytolith spectra produced by woody species from the most widespread ecosystem within the Zambezian regional centre of plant endemism, and now turn to the assessment of two questions raised by our results: how do the documented morphometric variables indicate taxonomic membership and what is the phytolith profile that hypothetically, if found in a geo-edaphic or archaeological context, would allow the scientist to infer plant community structure similar to the one seen today in Miombo woodlands. Over the last 10 years, the application of quantitative methods to study phytolith assemblages produced by modern plants has focused on questions such as the ability of specific morphotypes to discriminate subfamilies (Honaine et al., 2006), genera (Zucol, 1998, 2000) and species (Ball et al., 1999), the signal produced by C3 vs. C4 plant communities (Gallego and Distel, 2004), the grouping of taxonomically related species (Carnelli et al., 2004) and the connections between morphotype diversity and anatomical leaf features (Marx et al., 2004). The variables employed by these authors are the presence and frequency of types (Carnelli et al., 2004), the frequency of morphotypes expressed as a percentage of the total (Zucol, 1998, 2000; Gallego and Distel, 2004; Honaine et al., 2006), the ordination of both types and abundances (Marx et al., 2004) or simply the descriptive definition of keys (Ball et al., 1999). Their techniques have included PCA (Zucol, 1998, 2000; Honaine et al., 2006), CA (Carnelli et al., 2004; Gallego and Distel, 2004; Marx et al., 2004) and DA (Ball et al., 1999). In our case, PCA, CA and DA results support the hypothesis that a subset of orders and families can be clustered and identified on the basis of phytolith morphotype abundance and associations. To some extent, statistical analyses confirm what has been known for classic arboreal phytolith types for many years (Bozarth, 1992): they have very little taxonomic power because of redundancy across orders. In this respect, it is significant that none of the common types (85 % of the total) was flagged by PCA as a principal component. Yet, stating that arboreal phytoliths have no explanatory value would be a gross oversimplification. It is within the ‘uncommon’ and ‘unique’ categories (about 15 % of the total) that we see promise: blind, independent statistical testing and validation were able to identify up to 15 distinctive morphotypes produced by several members of derived clades among the Asterids (Asterales/Asteraceae; Gentianales/Apocynaceae; Ericales/ Ebenaceae; Myrsinaceae; Solanales/Solanaceae), some core eudicots (Rosales/Urticaceae; Caryophyllales/Amaranthaceae; Mercader et al. — Phytoliths from woody plants in Mozambique 3 9 5 8 1 6 10 4 7 2 109 Solanaceae Euphorbiaceae Apocynaceae Fabaceae Polygalaceae Musaceae Euphorbiaceae Annonaceae Fabaceae Fabaceae Fabaceae Bignoniaceae Fabaceae Fabaceae Combretaceae Fabaceae Urticaceae Fabaceae Asteraceae Fabaceae Annonaceae Arecaceae Euphorbiaceae Euphorbiaceae Amaranthaceae Dipterocarpaceae Fabaceae Asteraceae Apocynaceae 0 5 10 15 20 25 15 20 25 Rescaled linkage distance 2 3 6 1 7 5 4 Tabular ridged Tabular thin Clavate granulate Globular granulate oblong Globular folded Globular psilate large Blocky tuberculate Globular granulate large Globular tuberculate Tabular crenate Cylindroid large Blocky pilate Tabular scrobiculate Blocky polygonal Cylindroid columellate 0 5 10 Rescaled linkage distance F I G . 8. Dendrograms from cluster analysis (Ward’s method, Euclidean distance, by SPSS 15). Families clustered on the basis of specific morphotype frequency. Stem phytoliths only. Numbers on the far left indicate the cluster number. Malpighiales/Euphorbiaceae; Fabales/Fabaceae; Malvales/ Dipterocarpaceae, Sterculiaceae; Myrtales/Myrtaceae), monocots (Arecales/Arecaceae) and primitive monocots within the Magnolids (Magnoliales/Annonaceae) as arboreal groups that produce phytolith morphotypes with acceptable discriminatory capabilities. The phytolith profile studied here demonstrates that silicon is a low prominence mineral plant constituent in Miombo trees and bushes. This finding is in agreement with reported low values of silica concentrations among dicotyledonous plants, especially among the Fabales (Epstein, 1994, p. 12; Hodson et al., 2005, p. 1040; cf. Carnelli et al., 2001; Marx et al., 2004). Woody species from Niassa produce large phytoliths. Over half of our morphotypes are considerably larger than 50 mm, and, in fact, smaller types (,20 mm) are in a minority, making up about one-fifth of the total number of 110 Mercader et al. — Phytoliths from woody plants in Mozambique Selectively destructed ~50 % Fidelity preserved ~50 % (Weakly silicified types, thinwalled phytoliths, stomatal complex, hairs, hairbases) (Blocky, cylindroid, globular, tabular) Representation in total assemblage (%) 18 Common morphotypes (85 % of the total) 16 14 12 10 8 6 4 2 0 Stomatal Tracheary complex, elements hair, hairbases Globular psilate Globular granulate Globular echinate Blocky Cylindrous polygonal bulbous Blocky F I G . 9. Model predicting a selective destruction and preservation of arboreal phytoliths from Miombo ecosystems. The lower graph shows the ten most common phytolith groups and their percentage representation in the total phytolith assemblage. morphotypes. This finding indicates that extraction techniques that sieve sediments or use gravity sedimentation with a cut-off, discard point between 50.238 and 63.246 mm should not be used as these methodologies surely cannot extract phytoliths .50 mm. Another defining characteristic of Miombo phytoliths is their heavily pitted (decorated) textures, which are a natural feature of this population and not weathering markers left by taphonomic processes such as dissolution. With regard to contamination, we have observed instances in which stem specimens contained phytoliths known to be produced exclusively by leaf tissue or the grasses; therefore, these types can only be interpreted as foreign, unrelated silica particles (Tsartsidou et al., 2007: Fig. 7). Yet, the instances in which blatant contamination was detected were rare. Moreover, we used heavily polluted specimens (n ¼ 3) to test if an aggressive cleaning methodology could reduce impurity levels. We noticed that soaking and deflocculating overnight prior to cleaning and the use of extended, successive sonication cycles were able to cut down contamination rates by 60 (Ficus spp.) to 75 % (Dolichos kilimandscharicus), as deduced from both AIF differences for the same specimen and absolute counts of control targets in the same sample before and after cleaning (e.g. clusters of isodiametric cells exclusive to the leaf tissue). Yet, it should be borne in mind that, at least in our reference collection from Niassa, these are extreme situations, and that a specific stem phytolith sample has to be studied under the microscope to establish contamination on an individual basis before it can be concluded that contamination is an issue for that specific sample, or that contamination of all stem samples in a collection is prevalent. Detailed taphonomic analysis of phytoliths is beyond the scope of this study. Only the retrieval, quantification and especially the comparison of opal silica from local soils and sediments with the data presented here will establish the aspects of quality and source of bias in the regional fossil Mercader et al. — Phytoliths from woody plants in Mozambique record. Many filters govern the long-term preservation of phytoliths, including silica supply, the matrix geochemistry, the likelihood of immediate (and permanent) burial, reworking, the impact of silica recycling by living plants and the capacity of a phytolith morphotype to resist the changing physical and geochemical conditions that typify the highly dynamic and time-averaged nature of topsoils (Behrensmeyer et al., 2000, p. 107). Until a meticulous phytolith catalogue from modern soils is available, we can only suggest that the compositional fidelity in Miombo assemblages will probably be low. We foresee selective destruction of any silica body that is partially silicified or thin, which alone would bring about a loss of around 50 % of the total assemblage (Fig. 9). Morphotypes that may stand better chances at preservation include globular psilates, globular granulates and echinates, blocky types, cylinders and tabular shapes. To this segment that comprises about half the available silica produced by local arboreal plants, we would have to add grass silica for the Miombo phytolith spectrum to be comprehensive. Conclusions We have provided the first quantitative taxonomy of phytoliths for the largest phytochorion of sub-Saharan Africa. This taxonomy includes new types and is the most extensive phytolith key for any African ecoregion (41 families, 77 genera, 90 species). We contribute to filling the current information gap in woody phytoliths and explore their taxonomic value in paleoecological reconstruction through phytolith analysis. More specifically, we have presented evidence that Miombo woody species are hypervariable silica producers and their phytolith morphotypes are many and highly polymorphic. The taxonomic significance of phytolith types produced by indigenous trees and shrubs from this part of Africa is largely poor, but there are important exceptions that include several morphotypes produced by members of .10 families and orders. Lastly, this paper has put forward a model illustrative of the phytolithic signal that ‘Zambezian’ woody species are likely to leave behind in the fossil record: a skewed segment of the total phytolith spectrum favouring blocky, cylindroid, globular and tabular forms. S U P P L E M E N TARY D ATA Supplementary data are available online at www.aob. oxfordjournals.org/ and consist of a list of all the specimens processed in this study with individual counts for all samples. ACK N OW L E DG E M E N T S This work could have not been accomplished without Arianna Fogelman, Lourenço Thawe, Justin Sondergaard, Sofia Sondergaard, and the numerous workers, friends and authorities in Niassa. The authors thank the Department of Anthropology and Archaeology at Eduardo Mondlane University for the support, collegiality and encouragement, especially Professor Hilário Madiquida. Work in Niassa was conducted under two permits to J.M. from Eduardo Mondlane University and the Ministry of Education and Culture (03-2003 and 01-2007). Temporary export of materials 111 was conducted under ‘Certificate of Origin no. 0134’ from the Mozambican Chamber of Commerce, as well as the ‘Export License no. 24399’ from the Mozambican Customs Service. We thank the Canada Research Chairs programme and the Canada Foundation for Innovation for making much of this research possible through generous grants and research endowments (CFI grant no. 201550) to the lead author, and the Tropical Archaeology Laboratory at the University of Calgary, the Faculty of Social Sciences, Department of Archaeology and various internal programmes at the University of Calgary made available financial and logistical support to the authors. The Social Sciences and Humanities Research Council of Canada (File no. 410-2007-0697; CID: 148244), as well as the American Embassy in Maputo (Ambassador’s Fund for Cultural Preservation) assisted this project with essential monetary aid. The Department of Anthropology at the George Washington University and the Human Origins Program at the Smithsonian Institution provided institutional support. 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