Pollen of African Spermacoce species (Rubiaceae) Morphology and evolutionary aspects

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1 Grana ISSN: (Print) (Online) Journal homepage: Pollen of African Spermacoce species (Rubiaceae) Morphology and evolutionary aspects Steven Dessein, Suzy Huysmans, Elmar Robbrecht & Erik Smets To cite this article: Steven Dessein, Suzy Huysmans, Elmar Robbrecht & Erik Smets (2002) Pollen of African Spermacoce species (Rubiaceae) Morphology and evolutionary aspects, Grana, 41:2, 69-89, DOI: / To link to this article: Published online: 05 Nov Submit your article to this journal Article views: 821 View related articles Citing articles: 6 View citing articles Full Terms & Conditions of access and use can be found at

2 Grana 41: 69± 89, 2002 Pollen of African Spermacoce species (Rubiaceae) Morphology and evolutionary aspects STEVEN DESSEIN, SUZY HUYSMANS, ELMAR ROBBRECHT & ERIK SMETS Dessein, S., Huysmans, S., Robbrecht, E. & Smets, E Pollen of African Spermacoce species (Rubiaceae). Morphology and evolutionary aspects. ± Grana 41: 69± 89. Pollen morphology of 43 African species of the genus Spermacoce has been investigated by scanning electron and light microscopy. The genus is eurypalynous, which is re ected in the remarkable variation of almost all pollen characters. The average equatorial diameter ( E) ranges from 15.8 mm to mm. Grains are colporate or pororate. The number of apertures varies from 3 up to more than 25. The majority of species has apertures situated only at the equator (being zonoaperturate), but a few species have pantoaperturate grains. The endoaperture is generally an endocingulum, often with a secondary lolongate or lalongate thinning at the ectocolpus; endocolpi and endopores are also observed. The sexine is usually perforate, but eutectate, foveolate, and (micro)reticulate tecta were also found. Supratectal elements are present as granules, microspines or spines. The inner nexine surface is granular, often with irregular grooves (endocracks). Among native African species, nine pollen types are recognized mainly on the basis of pollen size, aperture morphology and tectum peculiarities. In two of the pantoaperturate types, apertures are in a con guration not yet recorded for the angiosperms in general. Some evolutionary trends are proposed that await veri cation by further systematic study. Pollen morphological characters have a high taxonomic value in the genus Spermacoce. They provide almost unique identi cation marks for the species, which enables sharpening of species boundaries. Small groups of related species often share the same pollen type. The genus Borreria, previously separated from Spermacoce on the basis of its fruit morphology only, is not supported by pollen data. Steven Dessein, Suzy Huysmans & Erik Smets, Laboratory of Plant Systematics, Institute of Botany and Microbiology, K.U.Leuven, Kasteelpark Arenberg 31, B-3001 Leuven; Belgium: Elmar Robbrecht, National Botanic Garden of Belgium, Domein van Bouchout, B-1860 Meise; Belgium. steven.dessein@bio.kuleuven.ac.be (Manuscript received 13 July 2001; accepted 11 April 2002) The Spermacoce-Borreria alliance ( Rubiaceae: Sperm- 1989, Deb & Dutta 1984, Sivarajan et al. 1987), is divided acoceae) is a large complex with a worldwide distribution in by others (e.g., Bacigalupo 1972, Steyermark 1972, 1974, the tropics and subtropics. The estimated number of species Bacigalupo & Cabral 1996) on the basis of peculiarities of varies between 150 and 250 ( Verdcourt 1989), depending on the fruit dehiscence. The segregated genus Borreria G.Mey. the authors. The plants typically grow in woodlands and is then characterized by having capsules with a septicidal grasslands, and are characterized by a herbaceous habit, opening and both fruit valves dehiscent, and Spermacoce mbriate stipules connected to the petioles, mostly small, sensu stricto by its fruits splitting into two valves, one isostylous owers arranged in compact lateral and terminal dehiscent and the other indehiscent (Meyer 1818). These in orescences, valvate bud aestivation, uni-ovulate ovary fruit characters are easy to observe, but no other features locules, dry capsular fruits, and presence of raphides. The seem to be correlated with it (cf. Verdcourt 1975, 1976, Deb group is, along with 18 smaller genera, placed in the tribe & Dutta 1984, Sivarajan et al. 1987). In the present article Spermacoceae, subfamily Rubioideae ( Robbrecht 1988). A we accept Verdcourt s view (1975) and relegate Borreria to molecular study of Andersson & Rova (1999) con rmed the the synonymy of Spermacoce. monophyly of the tribe, but the group was nested within Only few, limited studies exist on the pollen of Spermacoce. members of the tribe Hedyotideae, which makes the latter The earlier ones were part of broader studies on the phylogeny paraphyletic (see also Bremer et al. 1995, Natali et al. 1995, of Rubiaceae (e.g., Bremekamp 1952, Verdcourt 1958). Bremer 1996, Bremer & Manen 2000). For this reason, All reported that pollen of Spermacoce is multi-aperturate, Bremer ( 1996) proposed the Spermacoceae sensu lato, including but they did not fully survey the morphological variation the former tribes Hedyotideae, Knoxieae and Manettieae. within the genus. More recently, pollen studies of the In the present paper, the term Spermacoceae is used in its American representatives of Spermacoceae demonstrated the more traditional, narrow sense (cf. Robbrecht 1988). systematic value of pollen characters in the tribe. Pollen Generic delimitations within the complex have been characters were used to re-establish the genus Galianthe debated for almost two centuries. Spermacoce L. broadly (Cabral 1991, Pire & Cabral 1992, Pire 1997a) and to de ned by some authors (e.g., Verdcourt 1975, 1976, 1983, support a new subgeneric classi cation for the American

3 70 S. Dessein et al. â Ö Ö species of Psyllocarpus ( Kirkbride 1979) and Borreria variation in E-averages frequently exceeds 20%. Sometimes, ( Bacigalupo & Cabral 1996, Pire 1996, Cabral & Bacigalupo this variation can be explained in terms of intraspeci c 1999). Pollen morphology was also used to erect the genus variation, as is the case for Spermacoce phyteumoide s: var. Phylohydrax for the African and Madagascan Hydrophylax phyteumoides and var. caerulea have smaller pollen grains species (PuV 1986). Until now, pollen of the African than ``var. longituba. Verdcourt informally recognized the Spermacoce species was never investigated. latter variety on the herbarium sheets for its longer corolla The present study aims (1) to survey the pollen morpho- tube. In general there is a positive correlation in the study logy of the African representatives of Spermacoce, ( 2) to group between size of the corolla tube and pollen size discuss its signi cance in the taxonomy of the genus, and (3) (Fig. 1 A; r 2 =0.43; p<0.01): larger owers tend to produce to formulate a hypothesis for the evolution of pollen characters larger pollen grains. This correlation is also found in many within the genus. The project is part of the ongoing other groups and may be correlated with diverences in research of the rst author to document the biodiversity of nutrition supply (Muller 1979). Spermacoce in Africa. In the present study, however, the correlation between ower and pollen grain size is not strict. Flowers with a MATERIAL AND METHODS corolla tube smaller than 3 mm have pollen grains ranging from ca. 15 mm up to 60 mm, while medium sized owers This study is based on herbarium material from BR, K, WAG and (tube ca. 7 mm) show pollen grains between 55 mm and ZT (Table I ). Pollen of 92 specimens from 43 species were investi- 105 mm. Moreover, very variable species, such as Spermacoce gated (Table I). For the remaining African species (ca. 25 ) owering subvulgata, have corolla tubes ranging from 3 to 6 mm, but material in the above mentioned herbaria was not suycient to carry out palynological research. Due to the problematic delimitation of no correlated diverences are observed in the size of their several species of Spermacoce, we only selected specimens that fully pollen. Probably, the true correlation lies in the pollen vector correspond with the type specimen (if seen) or with the original size, rather than in the size of the owers. Although only a descriptions; additional comments on some problematic species/ few studies (cf. Muller 1979) have demonstrated that diverent specimens are provided ( Table I ). Species introduced to Africa are pollen vectors prefer diverent ranges of pollen size, it seems marked with an asterisk; the table also indicates the specimens used likely that this partly explains the considerable interspeci c for the illustrations. Mature ower buds were rehydrated in an Agepon (Agfa pollen size variation. Gevaert) solution (1:200), and dissected using a stereomicroscope. Another hypothesis to explain the pollen size variation is Pollen was acetolysed for 9 minutes in a heating block at 90ß C. the level of polyploidy. Higher levels of polyploidy may Pollen grains for SEM studies were suspended in ethanol (70%), express itself directly in a larger pollen size (Muller 1979). pipetted onto specimen stubs, air-dried and coated with gold with a Herbaceous Rubiaceae are known to have high levels of SPI-MODULE TM sputter coater. Observations were made under polyploidy (cf. Lewis 1965, Kiehn 1986). Kiehn ( 1986, 1995) a Jeol JSM-6400 SEM. Grains for LM studies were mounted in Kaiser s glycerin jelly. The slides were observed using a Leitz Dialux surveyed the chromosome numbers of the Rubiaceae; for the 20 with a 100 oil immersion or 40 objective lens. Equatorial Spermacoceae, the basic chromosome number is predomidiameter (E) was measured under LM in at least ten mature pollen nantly 14, and tetraploidy and hexaploidy originated several grains (magni cation 1000). We were not able to obtain accurate times within the tribe ( Kiehn 1986). Moreover, diverent measurements for the polar axis (P) under LM, since most grains ploidy levels are recorded for specimens of the same species; are suboblate. All other measurements were made on SEM-graphs. hence, giving support for the hypothesis that some of the To express the relative length of the colpi, we used the length intraspeci c pollen size variation is caused by diverences in colpi/polar axis rate multiplied by 100 (=LC/P). Broken pollen grains were obtained by shaking a pollen and glass bead suspension ploidy levels. as described by Huysmans et al. (1994). Terminology follows Punt In many genera of Rubiaceae, diverences in pollen size et al. (1999). may be explained by heterostyly (Huysmans et al. 1998, Dessein et al. 2000). In general, the brevistylous form has RESULTS larger pollen grains than the longistylous morph (cf. Ganders 1979). African Spermacoce species, however, are invariably Pollen characters Pollen morphology of African Spermacoce species is remarkably heterogeneous. In all pollen characters, the group reveals a variation that is usually only observed at higher systematic levels. This diversity is described and discussed below for the diverent diagnostic pollen characters and is illustrated by SEM-graphs. Detailed information at species level is presented in Table II. Size Pollen grain size of African Spermacoce species ranges from small to large, the average equatorial diameter ( E) varying from 15.8 mm in Spermacoce mauritiana to mm in S. ivorensis. The size variability within a single specimen is considerable (often exceeding 10%); within a species the homostylous, hence this hypothesis can not explain the intraspeci c variation observed. Shape P/E. ± In equatorial view, pollen shape is described by the P/E rate. In the study group, subprolate (P/E is 1.14± 1.33; Fig. 10), spheroidal (P/E is 0.88± 1.14; Figs. 11± 14) as well as suboblate ( P/E is 0.75± 0.88; Figs. 15± 16) and oblate (P/E is 0.50± 0.75; Fig. 17) pollen is found. The spheroidal condition can be further divided into oblate spheroidal (P/E is 0.88± 1) and prolate spheroidal (P/E is 1± 1.14). There is a negative correlation between the equatorial diameter and the P/E rate (Fig. 1 B; r 2 =0.29; p<0.01). The smaller the pollen grains the higher the P/E value. Spheroidal pollen grains, however, can be small as well as large.

4 Table I. Specimens examined including type- and gure references. Pollen of African Spermacoce species (Rubiaceae) 71 1 Spermacoce articularis L.f.: treated as a synonym of Spermacoce hispida L. by Verdcourt (1976) in FTEA and many others, but recognized again by Sivarajan et al. (1987). Native to Asia, but introduced in tropical Africa. 2 Cited in FTEA as Spermacoce hispida L. by Verdcourt (1976). 3 Spermacoce assurgens Ruiz & Pav.: There is much confusion about the identity of this species. It was treated under S. laevis Lam. by Verdcourt (1976 ) in FTEA and many others. Recently, Cabral & Bacigalupo (1999) placed S. assurgens in synonymy to Spermacoce remota Lam., which they transferred to Borreria subgenus Borreria section Borreria, series Laeves. Whether this is correct, needs con rmation; the pollen grains of the specimen studied here do not correspond with the pollen grains of S. remota (Pire 1996, treated under B. laevis (Lam.) Griseb.). 4 Spermacoce mauritiana Osia Gideon: the delimitation of this species has been debated for a long time, and it was often confused with Spermacoce ocymoides Burm.f. Verdcourt (1983 ) ± based on unpublished material of Gideon and Fosberg ± stated that ``the suggestedly cosmopolitan S. ocymoides is actually a complex of species distinguishable mainly on seed characters and published Gideon s name Spermacoce mauritianta (a substitute name for Borreria repens DC.) for the form with two calyx lobes. Cabral & Bacigalupo (1996), however, accept ``Borreria ocymoides as one variable species until more African and Asiatic specimens can be studied. The specimens investigated here are provided with two sepals (as all African species seen by the rst author). 5 The specimen investigated was labeled by Verdcourt as Spermacoce phyteumoides var. longituba. This name, however, is still unpublished. * Species introduced to Africa. Taxon Collection Country Herb. Type Figure Spermacoce annua Verdc. Mutimushi 3356 Zambia K 6 Fig. 25 *S. articularis L.f. 1, 2 Milne-Redhead & Taylor 7522 Tanzania BR 15 S. arvensis (Hiern) Good Bingham 8946 Zambia K 14 Pope, R-Smith & Goyder 2226 Zambia K Bidgood, Monasunki & Vollesen 1062 Tanzania BR Fig. 7 *S. assurgens Ruiz & Pav. 3 Faulkner 943 Tanzania BR 11 S. azurea Verdc. Bidgood, Mbago & Vollesen 2528 Tanzania K 14 Richards Tanzania BR Figs. 15, 27, 37 S. bambusicola (Berhaut) Vanden Berghen 6674 Senegal BR 16 J.-P.Lebrun & Stork Vanden Berghen 8522 Senegal BR Thomas 2731 Sierra Leone K Fig. 42 Adam Guinea BR S. chaetocephala DC. Berhaut 2933 Senegal BR 11 Leeuwenberg & Beek Cameroon BR Leippert 5071 Kenya BR Lisowski B-1172 Tchad BR S. congensis (Bremek.) Verdc. Pawek Malawi BR 15 Fig. 41 S. deserti N.E.Br. Skarpe S-444 Botswana K 17 Fig. 44 S. dibrachiata Oliv. Bidgood, Mbago & Vollesen 2695 Tanzania BR 14 Figs. 8, 17, 20, 46, 49 Lejeune 197 D.R. Congo BR Chapman 272 Malawi BR Troupin Rwanda BR Pereira, Sarmento & Marques 1829 Mozambique BR Lewalle 1694 Burundi BR Saintenoy 162 Burundi BR S. lifolia (Schumach. & Thonn.) de Wilde & de Wilde-Duyfjes 3091 Cameroon BR 12 Figs J.-P.Lebrun & Stork Geerling & Bokdam 984 Ivory Coast BR S. liformis Hiern Dalziel 212 Nigeria K 11 Fig. 12 S. lituba ( K.Schum.) Verdc. Faulkner 2168 Tanzania BR 17 Drummond & Hemsley 3632 Tanzania BR Figs. 6, 13 S. hepperana Verdc. Lejoly 85/314 Burkina Faso BR 11 S. hockii (De Wild.) Dessein Homble 796 D.R. Congo BR 14 Schaijes 1467 D.R. Congo BR Fig. 43 Schaijes 1960 D.R. Congo BR Duvigneaud & Timperman B-2627 D.R. Congo BR S. huillensis (Hiern) Good Quarre 1957 D.R. Congo BR 15 Hess-Wyss 52/584 Angola ZT S. intricans (Hepper) H.M.Burkill Bos, van der Laan & Nzabi Gabon WAG?17 S. ivorensis Govaerts Geerling & Bokdam 1701 Ivory Coast BR 16 S. kirkii (Hiern) Verdc. Schlechter Mozambique BR 15 Fig. 21 *S. latifolia Aubl. Lisowski D.R. Congo BR 2 Figs. 19, 32 Hepper & Maley 7760 Ivory Coast BR S. latituba ( K.Schum.) Verdc. Scott s.n. Malawi K 15 Figs. 28, 39 McClounie 84 Zambia K

5 72 S. Dessein et al. Table I. (Continued). Taxon Collection Country Herb. Type Figure S. mauritiana Osia Gideon 4 Evrard 157 D.R. Congo BR 1 Quarre 7867B D.R. Congo BR Vanden Berghen 9164 Senegal BR S. natalensis Hochst. Polhill & Paulo 1419 Tanzania BR 1 Figs. 3, 10, 18, 35 Thulin & Mhoro 3128 Tanzania WAG Fig. 2 S. octodon (Hepper) Hakki de Wilde 992 Ivory Coast BR 12 Lely 522 Nigeria K Figs. 23, 36 S. phyteuma Schweinf. ex Hiern Simpson 7325 Sudan K 6 Figs. 9, 26, 33± 34 S. phyteumoides Verdc. var. King 3 Zambia BR 14 Figs. 16, 45, 50 phyteumoides S. phyteumoides Verdc. var. Richards 8431 Tanzania K Fig. 38 caerulea Verdc. S. phyteumoides Verdc. ``var. Carter, Abdullah & Newton 2582 Tanzania K Fig. 22 longituba 5 S. princeae ( K.Schum.) Verdc. Ngoundai 250 Tanzania BR 17 Fig. 40 Huxley 84 Tanzania BR S. pusilla Wall. Malaisse 9691 D.R. Congo BR 11 S. quadrisulcata (Bremek.) Verdc. Schmitz 7228 D.R. Congo BR 11 Homble 930 D.R. Congo BR Troupin 1407 D.R. Congo BR S. radiata (DC.) Hiern Berhaut 435 Senegal BR 11 Robbrecht & Leman 3377 Niger BR Vanden Berghen 6197 Senegal BR S. ruelliae DC. Leeuwenberg 2323 Ivory Coast BR 17 van den Bossche 3473SerI Togo BR S. senensis ( Klotzsch) Hiern Polhill & Paulo 2347 Tanzania BR 15 Fig. 14 Tanner 659 Tanzania BR S. spermacocina ( K.Schum.) de Wilde 8518 Cameroon BR?17 Bridson & PuV van Eijnatten 2077 Nigeria BR S. sphaerostigma (A.Rich.) Oliv. Reekmans Burundi BR 17 Bredo 1487 D.R. Congo BR Michel 3058 D.R. Congo BR Drake 92 Sudan BR S. stachydea DC. Vanden Berghen 9184 Senegal BR 17 Figs. 29± 30 Vanden Berghen 6119 Senegal BR S. stipularis Dessein Milne-Redhead 4338 Zambia K 14 Malaisse & Robbrecht 1996 R.D. Congo BR Bamps, Martins & Maia 4175 Angola BR S. subvulgata ( K.Schum.) Lewalle 5606 Burundi BR 15 Fig. 47 J.G.Garcia Lisowski D.R. Congo BR Bredo 2262 D.R. Congo BR Lisowski, Malaisse & Symoens 4139 D.R. Congo BR Schlieben 2321 Tanzania BR S. taylorii Verdc. Milne-Redhead & Taylor 8821 Tanzania BR 15 Fig. 5 *S. tenuior L. Humblot 599 Madagascar K 1 S. tenuissima Hiern Fay 3445 R.C. Africa BR 12 Figs. 48, 53± 54 S. terminali ora Good. Gossweiler 2347 Angola BR 13 S. thymoidea (Hiern) Verdc. Pearson 2772 Angola K 13 Figs. 57± 58 Hess-Wyss 52/1798 Angola ZT Figs. 24, 55± 56 *S. verticillata L. Chevalier 1026 Sudan BR 3 Figs. 4, 11, 31 Dessein 24 Cultivated at BR BR ± ± Amb. In polar view, the pollen outline is usually circular Apertures and often lobed due to the longer columellae towards the Number. The number of colpi ranges from 3± 4 in centers of the mesocolpia or due to the thicker nexine around Spermacoce mauritiana ( Figs. 2± 3) to 16± 21 in S. dibrachiata the apertures (cf. below). Only Spermacoce natalensis and S. ( Fig. 8). The pantopororate species have up to 30 pores. The mauritiana have a triangular or quadrangular polar outline higher the number of colpi, the higher the intraspeci c (Figs. 2± 3). variation observed. There is a weak positive correlation

6 Table II. Some variable pollen morphological characters for each species studied. Pollen of African Spermacoce species (Rubiaceae) 73 Species are arranged by pollen type as discussed in the text. (x): number of specimens studied. Shape as seen in equatorial view: O=oblate; SO=suboblate; OS=oblate spheroidal; S=spheroidal; PS=prolate-spheroidal; SP=subprolate. Number of apertures: values between brackets were not found in all specimens investigated. Aperture type: PC=pantocolporate; PP=pantopororate; ZC=zonocolporate. Peculiarities: CM=colpus membrane; EP=equatorial plane. Types in Endo-column are discussed in the text. Apertures Wall ornamentation Type Species Size Shape Number Type Endo Peculiarities Sexine Nexine 1 S. mauritiana (3) 14-(15.8)-18 PS 3-4 ZC II perforate, margo of granules/ nely granular, endocracks microspines indistinct 1 S. natalensis (2) 14-(16.5)-19 SP 3-4 ZC II eutectate at apocolpium, nely granular, endocracks perforate at mesocolpium, indistinct or absent margo of granules 1 S. tenuior (1)* 15-(16.1)-17 PS-SP 6-8 ZC II perforate, margo of granules/ nely granular, endocracks microspines indistinct or absent 2 S. latifolia (2)* 44-(48.3)-50 SO-OS (7)-9-(11 ) ZC V perforate, granulate granular, broadô distinct endocracks 3 S. verticillata (2)* 23-(28.0)-30 OS (6-9) ZC IV perforate, granulate granular, narrowô distinct endocracks 6 S. annua (1) 62-(66.5)-74 S ca. 30 PP VI operculum microreticulate to reticulate, nely granular, no present microechinate endocracks 6 S. phyteuma (1) 80-(87.0)-90 S ca. 24 PP VI operculum perforate-microreticulate, nely granular, no present microechinate endocracks 11 S. assurgens (1)* 35-(36.8)-38 SO-OS 8-10 ZC II endocingulum perforate, granulate- granular, narrowô distinct indistinct microechinate endocracks 11 S. chaetocephala 38-(44.7)-52 SO-OS (9)-11 ZC II perforate, granulate granular, indistinct (4) endocracks 11 S. liformis (1) 30-(32.0)-34 S 9-10 ZC II columellae perforate, granulate granular, narrow irregular slightly endocracks longer in EP 11 S. hepperana (1) 42-(46.5)-52 SO-OS 9-11 ZC II columellae perforate, granulate nely granular, narrow slightly distinct or obscure longer in EP endocracks 11 S. pusilla (1) 35-(37.0)-3 9 SO-OS 8-10 ZC II perforate, granulate? 11 S. quadrisulcata 37-(42.3)-45 SO-OS (10-13 ) ZC II perforate, granulate granular, narrow indistinct (3) endocracks 11 S. radiata (3) 29-(36.2)-44 OS (9)-10- ZC II perforate, granulate granular, narrow indistinct (13) endocracks 12 S. lifolia (2) 50-(56.6)-64 S ca. 15 PC III colpi perforate, granulate to granular, narrow indistinct arranged in a microechinate endocracks loop 12 S. octodon (2) 37-(40.9)-45 S ca. 14 PC III colpi perforate, granulate to granular, narrow distinct or arranged in a microechinate obscure endocracks loop 12 S. tenuissima (1) 47-(54.1)-57 S ca. 15 PC III colpi perforate, granulate to granular, narrowô distinct arranged in a microechinate endocracks loop 13 S. terminali ora 52-(54.4)-57 S ca. 24 PC III colpi perforate, microechinate granular, numerous irregular (1) arranged in a endocracks spiral pattern 13 S. thymoidea (2) 50-(56.9)-63 S PC III CM granular, perforate, microechinate granular, numerous irregular colpi endocracks arranged in a spiral pattern 14 S. arvensis (3) 75-(81)-86 O (16)-17- ZC I columellae perforate to perforate-? (18) distinctly reticulate in mesocolpia, longer in EP microechinate, surface undulating 14 S. azurea (2) 62-(69.6)-76 O-SO (13)-15- ZC I columellae perforate to perforate- nely granular, broad (16) distinctly reticulate in mesocolpia, distinct endocracks longer in EP microechinate, surface undulating 14 S. dibrachiata (7) 71-(84.8)-96 O-SO (16-21 ) ZC I columellae perforate to perforate- nely granular, broadô deep distinctly reticulate in mesocolpia, endocracks longer in EP microechinate, surface undulating 14 S. hockii (4) 67-(72.4)-82 SO 13-(15 ) ZC I columellae perforate to perforate- nely granular, narrow longer in EP reticulate in mesocolpia, distinct endocracks microechinate, surface undulating 14 S. phyteumoides 65-(66.7)-69 O-SO ZC I columellae perforate to perforate- nely granular, broadô deep var. phyteumoides distinctly reticulate in mesocolpia, endocracks (1) longer in EP microechinate, surface undulating

7 74 S. Dessein et al. Table II. (Continued). Apertures Wall ornamentation Type Species Size Shape Number Type Endo Peculiarities Sexine Nexine 14 S. phyteumoides 68-(70.7)-73 O-SO ZC I columellae perforate to perforate- nely granular, broad var. caerulea (1) distinctly reticulate in mesocolpia, undeep endocracks longer in EP microechinate, surface undulating 14 S. phyteumoides 75-(83.2)-90 SO ZC I columellae perforate to perforate- nely granular, broad ``var. longituba somewhat reticulate in mesocolpia, undeep endocracks (1) longer in EP microechinate, surface undulating 14 S. stipularis (3) 75-(83.0)-92 O-SO (14)-15- ZC I columellae perforate-microreticulate, granular, broad distinct (17) distinctly microechinate endocracks longer in EP?15 S. articularis (1)* 72-(76.8)-82 SO ZC I/II CM granular; perforate, microechinate nely granular, indistinct colpiô loxocol- endocracks porate, nexine slightly thicker around ectoaperture 15 S. congensis (1) 95-(99.0)-10 5 SO ZC II microreticulate to reticulate, granular, indistinct microechinate endocracks 15 S. huillensis (2) 78-(80.0)-82 SO-OS 9-11 ZC? nexine perforate, microechinate? slightly thicker around ectoaperture 15 S. kirkii (1) 88-(97.0)-10 9 SO-OS ZC? CM granular; perforate-microreticulate,? nexine microechinate to echinate thicker around ectoaperture 15 S. latituba (2) 88-(99.2)-11 0 SO (10)-12- ZC I CM granular; perforate-microreticulate, granular, narrow deep (13) nexine microechinate to echinate endocracks thicker around ectoaperture 15 S. senensis (2) 75-(80.0)-84 SO-OS 11 ZC II CM granular; perforate-microreticulate, granular, indistinct nexine microechinate endocracks thicker around ectoaperture 15 S. subvulgata (5) 73-(86.6)-94 SO-OS 10-(12 ) ZC I/II CM granular; perforate-microreticulate, granular, narrow indistinct nexine microechinate endocracks thicker around ectoaperture 15 S. taylorii (1) 100-(105.3)-11 0 SO ZC II nexine Microreticulate to reticulate, granular, narrow indistinct thicker microechinate endocracks around ectoaperture 16 S. bambusicola (4) 74-(90.0)-10 5 O-SO (13)-16 ZC II columellae perforate-foveolate, margins nely granular, very broad longer in EP of perforations bordered, distinct or obscure echinate endocracks 16 S. ivorensis (1) 105-(115.5)-12 5 OS ZC? columellae perforate, margins of? longer in EP perforations bordered, echinate 17 S. deserti (1) 58-(62.0)-68 SO ZC II columellae perforate, granulate to granular, narrowô distinct longer in EP microechinate endocracks 17 S. lituba (2) 77-(81.2)-87 SO-OS 12-(14 ) ZC? columellae perforate, microechinate to? longer in EP echinate?17 S. intricans (1) 70-(73.2)-76 SO 9-10 ZC? columellae perforate, granulate to? slightly microechinate longer in EP 17 S. princeae (2) 63-(71.9)-87 SO-OS ZC II columellae perforate-microreticulate, nely granular, narrow deep longer in EP granulate to microechinate endocracks 17 S. ruelliae (2) 74-(79.1)-90 SO-OS (13)-15- ZC II columellae perforate-microreticulate, granular, broad distinct (16) longer in EP (micro)echinate endocracks?17 S. spermacocina 64-(70.1)-77 OS 8-9 ZC II columellae perforate, granulate to nely granular, indistinct (2) slightly microechinate endocracks longer in EP 17 S. sphaerostigma 82-(91.0)-10 3 SO 11-(14 ) ZC II columellae perforate, microechinate to granular, no endocracks (4) longer in EP echinate 17 S. stachydea (2) 72-(81.7)-91 SO-OS (12)-13- ZC II columellae perforate, (micro)echinate granular, narrow distinct (15) longer in EP endocracks

8 Pollen of African Spermacoce species (Rubiaceae) 75 Fig. 1. Correlation analyzes between diverent pollen and ower characters. (A) Correlation between corolla tube size and pollen size (r 2 = 0.43; p<0.01); S. ivorensis was excluded because of its exceptional long corolla tube. (B) Correlation between P/E index and pollen grain size (r 2 =0.29; p<0.01). (C ) Correlation between number of apertures and pollen size (r 2 =0.14; p<0.01). (D) Correlation between number of apertures and pollen size with exclusion of the pantoaperturate species (r 2 =0.43; p<0.01). ± ± ± between pollen size and number of apertures (Fig. 1 C; r 2 = Position. In most species, the apertures are ordered along 0.14; p<0.01). However, the pantoaperturate species have the equator (zonoaperturate; Figs. 10± 17), Spermacoce phymany more apertures than can be expected from their size. teuma and S. annua are pantoaperturate, the ectopores being This is not surprising if we realize that the surface where the evenly spread over the pollen surface ( Fig. 9). Pire (1996: apertures can originate is much larger than for equally sized 422) noted in some Borreria species ``a tendency of the zonoaperturate species. Disregarding the pantoaperturate apertures to drift away from the equatorial plane; the apertu- species, the positive correlation between number of apertures ral plane appears as suvering a torsion due to the presence and pollen size is strong (Fig. 1 D; r 2 =0.43; p<0.01 ). of one or two pairs of convergent colpi. We clearly observed This multi-aperturate condition is apomorphic within the such loxocolporate colpi in Spermacoce articularis; in other family Rubiaceae, the 3-colporate pollen type being plesiomorphic species, e.g., S. chaetocephala, it was only sporadically (cf. Robbrecht 1988). Other genera of the tribe observed. Spermacoceae also have multi-aperturate grains (Bremekamp Two remarkable new colpi arrangements were also 1952, Verdcourt 1958, Kirkbride 1979, Pire & Cabral 1992, observed. The rst type, with the colpi arranged in a looplike Pire 1997 a, b), but it is rarely found in other Rubiaceae pattern, similar to the line on a tennis ball, is found except in the tribe Rubieae (Bremekamp 1952). In this tribe, in Spermacoce lifolia, S. octodon, and S. tenuissima however, the number of colpi is less variable and mostly ( Figs. 51± 52). The second type, where the short colpi are xed at 6 to 8 (Huysmans, pers. com.). arranged in a spiral pattern (Figs. 55± 56), characterizes Type. Apertures of Spermacoce are almost always compound, Spermacoce terminali ora and S. thymoidea. To our knowledge these two pollen types have not been previously i.e. built up by two or more components that are observed in angiosperms. The second type can be considered situated in more than one layer of the pollen wall. In the as an intermediate form between zonoaperturate and panto- species studied the apertures usually consist of an ectocolpus porate grains. An in-depth morphological and ontogenetic and an endocingulum (e.g., S. dibrachiata). In Spermacoce study is needed to further clarify these remarkable pollen verticillata and S. latifolia the endoaperture is a colpus. Both types. species, however, are most probably introduced from America. Spermacoce annua and S. phyteuma are character- Ectoaperture. As mentioned above, the ectoaperture is a ized by ecto- and endopores. colpus in most species ( Figs. 18± 24). The length of the colpi

9 76 S. Dessein et al. Figs. 2± 9. Polar views of Spermacoce pollen grains. (2) 3-colporate grain, slightly triangular in outline, tectum eutectate and psilate (S. natalensis). (3) 4-colporate grain, sub-quadrangular in outline (S. natalensis). (4) 7-colporate grain, tectum perforate (S. verticillata). (5) 10-colporate grain, notice the elevation of the sexine around the ectoapertures (arrows), tectum microreticulate (S. taylorii ). (6) 11-colporate grain, columellae longer in the equatorial plane, tectum perforate (S. lituba). (7) 13-colporate grain, columellae longer in equatorial plane, tectum perforate-microreticulate (S. arvensis). (8) 19-colporate grain, columellae longer in equatorial plane, tectum perforate (S. dibrachiata). (9) pantopororate grain with ca. 24 apertures, tectum perforate-microreticulate and microechinate (S. phyteuma).

10 Pollen of African Spermacoce species (Rubiaceae) 77 Figs. 10± 17. Equatorial views of Spermacoce pollen grains. (10) grain subprolate, margo of granules around ectoaperture (S. natalensis). (11) grain prolate-spheroidal (S. verticillata). (12) grain spheroidal, columellae in equatorial plane slightly longer (S. liformis). (13) grain suboblate, columellae longer in equatorial plane (S. lituba). (14) grain oblate-spheroidal, nexine thickened around ectoapertures forming a distinct margo, colpus membrane beset with large sexine particles (S. senensis). (15) grain suboblate, columellae longer in equatorial plane (S. azurea). (16) grain suboblate, columellae longer in equatorial plane, margins of colpi beset with microspines (S. phyteumoides). (17) oblate grain, columellae longer in equatorial plane, margins of colpi beset with microspines (S. dibrachiata).

11 78 S. Dessein et al. Figs. 18± 26. Morphology of ectoapertures of Spermacoce pollen grains. (18) slit-like colpus with margo of granules (S. natalensis). (19) slit-like colpus, sexine undiverentiated (S. latifolia). (20) slit-like colpus, margins beset with microspines, columellae longer in equatorial plane (S. dibrachiata). (21) colpus with margo of thickened nexine, colpus membrane beset with sexine particles (S. kirkii ). (22) slit like apertures with columellae slightly elongated in mesocolpium (S. phyteumoides). (23) detail of short colpus with margins beset with microspines (S. octodon). (24) short, spool-shaped aperture, colpus membrane beset with sexine particles (S. thymoidea). (25) three pores with operculum (S. annua). (26) pore with operculum of sexine particles (S. phyteuma).

12 Pollen of African Spermacoce species (Rubiaceae) compared with the polar axis (LC/P) ranges from 6 in Spermacoce terminali ora to 62 in S. tenuior. The colpi are often slit-like (Figs. 18± 21), but sometimes more widened (Fig. 24 ). In the latter case, there is often a gap in the colpus membrane where the ecto- and endoapertures overlap. If present, the colpus membrane is beset with large cubicshaped elements. The margins of the ectocolpus are often beset with microspines (Figs. 20, 23 ). Sometimes, the exine around the colpi is diverentiated (Figs. 18, 20± 22). Most commonly, the columellae are longer in the equatorial zone, but a thicker nexine around the apertures and the presence of granules around the colpi (Fig. 18 ) were also observed. These features are further discussed below. The pantopororate species have pores up to 4 mm in diameter (Figs. 25± 26). An operculum that covers the whole pore is present. In Spermacoce phyteuma it appears as an aggregate of angular, sexinous elements intermingled with smaller particles (Fig. 26); in S. annua it is made up of a granular aggregate that bears a central spine (Fig. 25). Endoaperture. ± The endoaperture is mostly an endocingulum, a ring-shaped endoaperture lying at the equatorial plane (Figs. 27, 29 ). The width of the endocingulum ranges from 1/3 to 2/3 of the length of the ectocolpi and often there are two triangular extensions (horns) in each mesocolpium. The inner surface is smooth or nely granular. Within the endocingulum, there is an additional thinning of the nexine at the ectocolpi. These thinnings are lalongate (Figs. 29± 30) or lolongate (Figs. 27± 28 ). In the former case, the thinning is oval- or diamond-shaped, and in the cut-aways, the surface is granular; in the latter case, the nexine abruptly declines near the ectocolpus and the surface becomes rough. Sometimes, this thinning is bordered by a granular thickening of the nexine within the endocingulum. In Spermacoce princeae, the endoaperture is not always continuous, the structure being disrupted by endocolpi that are not laterally fused. This transition between endocolpi and endocingulum has already been observed in other Rubiaceae (Dessein et al. 2000). In the species with a loop-like colpus arrangement, a continuous endoaperture connecting the ectocolpi is observed (Figs. 53± 54 ). It cannot be named an endocingulum, since it is not situated at the equatorial plane. In each mesocolpium, two broad extensions are continuous with the pattern of endocracks. An additional, diamond-shaped thinning within this endopattern is present at the ectocolpus. In the cutaways a granular layer becomes visible. An equally complex endopattern is found in Spermacoce thymoidea and S. terminali ora (Figs. 57± 58 ), where the ca. 24 colpi are interconnected by an irregular pattern of nexine thinnings: between two adjacent colpi a V-shaped or straight thinning of the nexine is present, with a triangular extension on one or both sides. A second, asymmetrical endocolpus perpendicular to the rst one can be present, often with branching tips. Around the ectocolpus, there is an oval thinning, revealing a perforated, granular layer. The endopores of Spermacoce phyteuma and S. annua are not distinct. In Spermacoce annua, it is only visible as a radiating pattern of ne endocracks within the inner surface of the nexine surrounding the ectopore; in S. phyteuma 79 (Figs. 33± 34 ), the surface of the nexine enclosing the ectopore is pitted and coarser than the surrounding nexine. The lalongate endocolpus of Spermacoce verticillata is bordered by two islands of thickened nexine but the ends are vaguely delimited and more or less continuous with the endocracks (Fig. 31). In Spermacoce latifolia, an indistinct lolongate endocolpus is present (Fig. 32). In conclusion six types of endoapertures can be distinguished: Type I endocingulum with additional lolongate thinnings (Figs. 27, 28 ) Type II endocingulum with additional lalongate thinnings (Figs. 29, 30 ) Type III endopattern comprising an irregular pattern of nexine thinnings between the ectocolpi (Figs. 53, 54, 57, 58) Type IV lalongate endocolpus (Fig. 31) Type V lolongate endocolpus (Fig. 32 ) Type VI endopore (Figs. 33, 34 ) Sexine ornamentation The variation in sexine patterns within Spermacoce is considerable. The majority of species, however, have a perforated tectum. Perforation size ranges from 0.1 mm to 1 mm, and perforation density is species dependent (Figs. 36± 40 ). In some species, small, circular perforations are intermingled with larger ones. In other species (e.g., S. latituba), there is a continuous transition into microreticulate tecta (Fig. 40). This character state is indicated as ``perforatemicroreticulate in Table II. A true microreticulate to reticulate tectum (muri narrower than lumina; Fig. 41 ) only occurs in Spermacoce annua, S. congensis, and S. taylorii. The tectum of Spermacoce bambusicola tends to be foveolate (Fig. 42). In this species and in Spermacoce ivorensis the margins of the perforations are distinctly thickened. There is often a considerable diverence between the sexine pattern observed at the mesocolpium and at the apocolpium. In Spermacoce natalensis, for example, the tectum is eutectate at the apocolpium and perforate at the mesocolpium. In Spermacoce dibrachiata the perforations are more elongated and much larger at the mesocolpium than at the apocolpium, the larger perforations being intermingled with smaller ones. The sexine pattern in which we have large lumina (often exceeding 1 mm) intermingled with small perforations with muri broader and smaller than the enclosed lumina is termed perforate-reticulate in Table II (cf. mesocolpia of Figs. 15± 17). We preferred not to use the term heterobrochate because it refers to a true reticulate pattern (Punt et al. 1999), which is not the case here. In a number of species (e.g., S. azurea, S. dibrachiata) the tectum is undulating in the apocolpium (Fig. 38). The tectum is always beset with supratectal elements, except for Spermacoce natalensis, S. mauritiana, and S. tenuior where the apocolpium is smooth or slightly scabrate (Fig. 35). The supratectal elements can be granules, microspines or spines. They are scattered over the pollen surface, or more rarely restricted to the zone around the apertures to form a margo of granules or microspines (Fig. 18).

13 80 S. Dessein et al. Figs. 27± 34. Endoaperture morphology of Spermacoce pollen grains. (27) inner view of a broken pollen grain showing endocingulum with additional lolongate thinnings at the ectoapertures (TE ) and in each mesocolpium an extension of the endocingulum (EE); notice the thickening of the nexine and the elongation of the columellae towards (arrow) the equatorial plane (S. azurea). (28) detail of additional lolongate thinning within endocingulum (S. latituba). (29) inside of pollen fragment with an endocingulum; nexine surface granular with numerous endocracks (S. stachydea). (30) detail of lalongate thinning within endocingulum (detail of 29). (31) detail of lalongate endocolpus with two islands of thickened nexine (TN) around endoaperture (S. verticillata). (32) detail of indistinct lolongate endocolpus (S. latifolia). (33) inside view at pollen half showing endopori (S. phyteuma). (34) detail of two endopori (detail of 33).

14 Pollen of African Spermacoce species (Rubiaceae) 81 Figs. 35± 42. Ornamentation of the tectum of Spermacoce pollen grains. (35) detail of apocolpium, eutectate (S. natalensis). (36) detail of apocolpium, tectum with small perforations, granulate (S. octodon). (37) detail of apocolpium, tectum with large, elongated perforations, micro-echinate (S. azurea). (38) detail of apocolpium, tectum surface undulating, perforations large, micro-echinate (S. phyteumoides). (39) detail of apocolpium, tectum perforate-microreticulate, echinate (S. latituba). (40) detail of mesocolpium, tectum perforate-microreticulate, small perforations intermingled with larger ones, granulate to micro-echinate (S. princeae). (41) detail of mesocolpium, tectum microreticulate to reticulate, micro-echinate (S. congensis). (42) detail of apocolpium, tectum perforate to foveolate, margins of perforations thickened, (micro-)echinate (S. bambusicola).

15 82 S. Dessein et al. Columellae Columellae are always present and well developed (Figs. 43± 46 ). Their length ranges from 0.2 to 2.6 mm at the apocolpium. In many species, the columellae are longer towards the centers of the mesocolpia, resulting in a protruding equatorial zone (Fig. 44 ). Nexine The nexine is fairly thick ranging from 0.3 to 1.7 mm at the apocolpium. The inner surface of the nexine is nely or coarsely granular. Endocracks are mostly present; they can be narrow and super cial (Fig. 47 ), narrow and distinct (Fig. 48 ) or broad and deep (Figs. 49± 50 ). Endocracks are mostly connected to the extensions of the endocingulum, but are absent in the zones between these extensions. In some species, the nexine is gradually thickened towards the equatorial plane (Fig. 27), in other species the nexine is distinctly thickened around the ectoapertures resulting in a protruding zone around the ectocolpi (Figs. 14, 21 ). The sexine/nexine rate varies between 0.9 and 2.1 in the apocolpium, but typically shows a value around 1.5. The value is strongly in uenced by the position of the measurement (even within the apocolpium) and is thus of minor importance in the characterization of the pollen grains. Pollen types Pollen of Spermacoce is so variable and the variation for each character so continuous, that it is diycult to propose a matching typology without recognizing a large number of types. However, to make this study more compatible with the work of Pire (1996), we propose a typology based on the same characters she used: pollen size, aperture number, aperture position, relative length of the ectoaperture, and endoaperture type. In the key below, we also include the pollen types found among the American representatives of the Spermacoce/Borreria complex; the type numbers used correspond with the types of Pire (1996). Description of pollen types Only the pollen types found among species present in Africa are described here. The descriptions are based on the African material only. For a detailed description of the other pollen types keyed out below, see Pire (1996). Type 1 (Figs. 2± 3, 10, 18, 35) Pollen zonocolporate (3± 4) or (6± 8), mean E 15.8± 16.5 mm; mean P/E rate 1.1± 1.2 (prolate-spheroidal, subprolate); polar outline triangular, quadrangular to almost circular. Ectocolpus long (LC/P 53± 62 ), narrow, slightly sunken. Endoaperture narrow endocingulum. Tectum perforate to eutectate at apocolpium; margo of granules or microspines. Inner nexine surface nely granular. Species included: 3± 4 colporate: S. mauritiana, S. natalensis. 6± 8 colporate: S. tenuior. Remark: Other species with same pollen type listed by Pire (1996). Type 2 (Figs. 19, 32) Pollen zonocolporate (7± 11), mean E 48.3 mm; mean P/E rate 0.88 (suboblate, oblate-spheroidal ); polar outline circular. Ectocolpus long (LC/P 38 ), narrow, slightly sunken. Endoaperture lolongate. Tectum perforate, uniformly granulate. Inner nexine surface nely granular with very broad, irregular endocracks. Species included: S. latifolia. Remark: Other species with same pollen type listed by Pire (1996). Type 3 (Figs. 4, 11, 31) Pollen zonocolporate (6± 9), mean E ca mm; mean P/E rate 0.95 (oblate-spheroidal ); polar outline circular. Ectocolpus short (LC/P 20), narrow, slightly sunken. Endoaperture lalongate. Tectum perforate, uniformly granulate. Inner nexine surface granular with numerous endocracks. Species included: S. verticillata. Remark: Other species with same pollen type listed by Pire (1996). Type 6 (Figs. 9, 25± 26, 33± 34 ) Pollen pantopororate (24± 30 ), mean E 66.5± 87.0 mm; mean P/E rate ca. 1 (spheroidal ); polar outline circular. Ectopore 2± 5 mm in diameter (LC/P 4.5± 5), operculum present. Endoaperture an indistinct endopore. Tectum perforatemicroreticulate or (micro)reticulate, microspines sparsely present on whole surface. Inner nexine surface nely granular, endocracks absent. Species included: S. annua, S. phyteuma. Remarks: Other species with same pollen type listed by Pire (1996). Although included in pollen type 6 of Pire (1996), Figs. 43± 50. Pollen wall strati cation and morphology of inner nexine surface of Spermacoce pollen grains. (43) wall strati cation at apocolpium showing nexine, row of short columellae and tectum with microspines; note regular endocracks in nexine surface (S. hockii ). (44) broken pollen wall at mesocolpium showing the elongation of the columellae (S. deserti). (45) cross section of pollen wall in mesocolpium showing from top to bottom: tectum with microspines (T), columellae (C), nexine (N ), endocingulum (E), lolongate thinning within endocingulum (TE), extensions of endocingulum (EE ) and nexine surface with endocracks (NE) (S. phyteumoides). (46) detail of strati cation: from top to bottom: perforated tectum with microspines (T ), columellae (C ), and nexine (N ); note granules on nexine (S. dibrachiata). (47) inner surface of granular nexine with indistinct endocracks (S. subvulgata ). (48) inner surface of granular nexine with distinct, narrow endocracks (S. tenuissima). (49) inner surface of nely granular nexine with broad deep endocracks (S. dibrachiata). (50) inner surface of nely granular nexine with broad deep endocracks (S. phyteumoides).

16 Pollen of African Spermacoce species (Rubiaceae) the pollen described here are larger and the apertures more numerous. Type 11 (Fig. 12) Pollen zonocolporate (8± 13 ), mean E 32.0± 46.5 mm; mean P/E rate 0.80± 1.00 (suboblate, oblate-spheroidal ); polar outline circular. Ectocolpus short (LC/P 15± 25 ), narrow, slightly sunken. Endoaperture endocingulum with two horns in each mesocolpium. Tectum perforate, granules (or microspines) 83 uniformly present. Inner nexine surface nely granular with numerous narrow endocracks. Species included: S. assurgens, S. chaetocephala, S. liformis, S. hepperana, S. pusilla, S. quadrisulcata, S. radiata. Remark: Other species with same pollen type listed by Pire (1996). Type 12 (Figs. 23, 36, 48, 51± 54) Pollen pantocolporate (ca. 15 ), E 40.9± 56.6 mm; mean P/E

17 84 S. Dessein et al. rate ca. 1 (spheroidal ); polar outline circular. Ectocolpus short (LC/P 6± 14 ) and narrow. Endopattern complex, including an ``endocingulum with horns, an additional lalongate thinning of the nexine at the ectocolpus, and numerous, often deep endocracks. Tectum perforate, granules or microspines uniformly present. Inner nexine surface granular, but smooth within endocracks. Species included: S. lifolia, S. octodon, S. tenuissima. Remark: The exact number of apertures is diycult to determine. Type 13 (Figs. 24, 55± 58) Pollen pantocolporate (ca. 24), mean E 54.4± 56.9 mm; mean P/E rate ca. 1 (spheroidal ); polar outline circular. Ectocolpus short (LC/P 6± 11) and narrow or somewhat widened, colpus membrane (if present) beset with granules. Endopattern complex, including an ``endocingulum with horns, an additional lalongate thinning of the nexine at the ectocolpus, and numerous endocracks. Tectum perforate, small perforations intermingled with larger ones, microspines uniformly present. Inner nexine surface granular, numerous endocracks. Species included: S. terminali ora, S. thymoidea. Remark: The exact number of apertures is diycult to determine. Type 14 (Figs. 7± 8, 15± 17, 20, 22, 27, 37± 38, 43, 45± 46, 49± 50) Pollen zonocolporate (13± 21), mean E 66.7± 84.8 mm; mean P/E rate 0.7± 0.8 (oblate, suboblate); polar outline circular, clearly lobed due to longer columellae in the equatorial zone. Ectocolpus relatively long (LC/P 24± 45 ), slit like, margins beset with microspines. Endoaperture a broad endocingulum with horns in the mesocolpia and with an additional lolongate thinning of the nexine at the ectocolpus. Tectum perforate, often perforate-reticulate at the mesocolpia, large perforations intermingled with smaller ones, surface often undulating; microspines uniformly present. Inner nexine surface nely granular with broad, undeep or deep, smooth endocracks. Species included: S. arvensis, S. azurea, S. dibrachiata, S. hockii, S. phyteumoides, S. stipularis. Remark: Pollen of Spermacoce dibrachiata divers from the other species included in its high number of colpi. Type 15 (Figs. 5, 14, 21, 28, 39, 41, 47 ) Pollen zonocolporate (9± 14 ), mean E 76.8± mm; mean P/E rate 0.82± 0.88 (suboblate, rarely oblate-spheroidal ); polar outline circular, slightly or strongly lobed due to thickened nexine around ectocolpi. Ectocolpus short (LC/P 10± 23) and relatively broad, colpus membrane (if present) beset with large cubic-shaped particles; nexine thickened around the ectocolpus, forming a distinct margo. Endoaperture a broad endocingulum with an additional lalongate or lolongate thinning of the nexine at the ectoaperture. Tectum perforate or perforate-microreticulate, rarely reticulate; margins of the perforations sometimes slightly thickened; microspines or spines uniformly present. Inner nexine surface granular with numerous, often indistinct endocracks. Species included: S. congensis, S. huillensis, S. kirkii, S. latituba, S. senensis, S. subvulgata, S. taylorii. Tentatively included: S. articularis. We found only one African collection with suycient owers to carry out palynological research; the nexine around the ectocolpi is thickened, but only slightly so. Remark: In S. congensis, the margo is not distinct, but it ts very well within this pollen type for all other characters. Type 16 (Fig. 42 ) Pollen zonocolporate (13± 18), mean E 90± mm; mean P/E rate 0.7± 0.9 (oblate, oblate-spheroidal ); polar outline circular, lobed due to longer columellae in the equatorial plane. Ectocolpus short (LC/P 14.6± 24.6), slit like. Endoaperture a broad endocingulum with horns in the mesocolpia and with a rather indistinct lalongate thinning at the ectocolpus. Tectum perforate or foveolate, margins of perforations thickened, spines uniformly present. Inner nexine surface granular with broad, undeep, smooth endocracks. Species included: S. bambusicola, S. ivorensis. Type 17 (Figs. 6, 13, 29± 30, 40, 44) Pollen zonocolporate [(8± 10 )± 11± 16 ], mean E 62.0± 91.0 mm; mean P/E rate 0.8± 0.92 (suboblate, rarely oblate-spheroidal ); polar outline circular, often (slightly) lobed due to longer columellae at the equatorial plane. Ectocolpus relatively short (LC/P 18± 24), slit like. Endoaperture a broad endocingulum with or without horns at the mesocolpia but always with an additional, lalongate thinning at the ectocolpus. Tectum perforate or perforate-microreticulate, large perforations often intermingled with smaller ones; microspines or spines uniformly present. Inner nexine surface granular with or without distinct endocracks. Species included: S. deserti, S. lituba, S. princeae, S. ruelliae, S. sphaerostigma, S. stachydea. Tentatively included: S. intricans and S. spermacocina. Both diver from the other species included in the lower number Figs. 51± 58. Detailed morphology of pollen types 12 & 13 of Spermacoce. (51) pollen grain of type 12 showing two rows of ectocolpi (S. lifolia). (52) diverent view of same pollen grain as in (51 ) showing colpi arranged in a loop. (53) view of inner side of an half of pollen showing complex endopattern with an ``endocingulum (E ), lalongate thinnings within endocingulum (TE), extensions of endocingulum (EE), and nexine (NE ) surface with numerous endocracks (S. tenuissima). (54) Detail of (53). (55) pollen grain of type 13 showing colpi arranged in a spiral (S. thymoidea). (56) diverent view of same pollen grain as in (55 ). (57) view of inner side of an half of pollen showing complex endopattern with cross-linked endocolpi, lalongate thinnings (TE ) within endocingulum (E ), extensions of endocingulum (EE), nexine surface (NE) with numerous endocracks (S. thymoidea). (58) detail of (57) showing the same elements.

18 Pollen of African Spermacoce species (Rubiaceae) 85