A New Heterophyllous Spermacoce Species (Rubiaceae) from the Marungu Highlands, Democratic Republic of the Congo Author(s): Steven Dessein, Elmar Robbrecht, Erik Smets Source: Novon: A Journal for Botanical Nomenclature, 16(2):231-234. 2006. Published By: Missouri Botanical Garden DOI: 10.3417/1055-3177(2006)16[231:ANHSSR]2.0.CO;2 URL: http://www.bioone.org/doi/ full/10.3417/1055-3177%282006%2916%5B231%3AANHSSR%5D2.0.CO %3B2 BioOne (www.bioone.org) is an electronic aggregator of bioscience research content, and the online home to over 160 journals and books published by not-for-profit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/ page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and noncommercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. A New Heterophyllous Spermacoce Species (Rubiaceae) from the Marungu Highlands, Democratic Republic of the Congo Steven Dessein and Elmar Robbrecht National Botanic Garden of Belgium, Domein van Bouchout, B-1860 Meise, Belgium. steven.dessein@br.fgov.be; elmar.robbrecht@br.fgov.be Erik Smets Laboratory of Plant Systematics, Katholieke Universiteit Leuven, Kasteelpark Arenberg 31, B-3001 Leuven, Belgium. erik.smets@bio.kuleuven.be ABSTRACT . Spermacoce heteromorpha Dessein (Rubiaceae, Spermacoceae) is newly described and illustrated. It grows on the Marungu highlands of the Democratic Republic of the Congo (D.R. Congo) at altitudes of 1800 to 1900 m. The species resembles the Tanzanian Spermacoce taylorii Verdcourt, from which it mainly differs in having terminal inflorescences, only slightly exserted anthers, and densely pubescent stems. Moreover, Spermacoce heteromorpha features marked heterophylly, with long leaves at the plant’s base and much shorter cauline leaves, a type of heterophylly rarely observed in Spermacoce or in the Rubiaceae as a whole. The finding of this species exemplifies the unique floristic richness of this underexplored part of D.R. Congo. Key words: Democratic Republic of the Congo, heterophylly, Marungu highlands, Rubiaceae, Spermacoce. Spermacoce L. is a pantropical genus of the family Rubiaceae comprising an estimated 275 species (Dessein et al., 2002; Harwood & Dessein, 2005). Tropical America, tropical Africa, and the northern part of Australia are the main centers of diversity. The genus is characterized by its herbaceous growth form, the fimbriate stipules connected to the petioles, the 4merous flowers arranged in compact lateral and/or terminal inflorescences, the bilocular ovaries with a single ovule per locule, the often pluriaperturate pollen grains, and the dry dehiscent fruits. Many botanists know Spermacoce as a genus of annual weeds of ruderal places. Typical examples are S. latifolia Aublet and S. verticillata L., two species presumably native to America, but introduced in Africa, Asia, and Australia. Narrow endemics, however, are an element of the genus with a comparable level of importance. Our study of Spermacoce from the high plateaus of the Zambezian regional center of endemism, for example, revealed the existence of endemic or disjunct Spermacoce species on the Angolan, Zambian, and Katangan high plateaus (Dessein et al., 2002, 2003). Within the Lisowski, Malaisse, and Symoens collection of POZG, which was recently put at our disposal, unicate Spermacoce specimens from the Marungu highlands (D.R. Congo) were found representing another narrow endemic as described below. HETEROPHYLLY Heterophylly is not uncommon among woody Rubiaceae (Robbrecht, 1988), but is rarely observed among the herbaceous representatives of the family. Within Spermacoce, it has only been recorded for S. hockii (De Wildeman) Dessein, a perennial from D.R. Congo (Dessein et al., 2003). In this species, long linear leaves develop from the woody plant base, while the cauline leaves are broader and much shorter. During field work in Zambia, we observed that several biannual or short-lived perennial Spermacoce species develop rosettes of basal leaves. This feature was observed in the field for S. dibrachiata Oliver, S. perennis Verdcourt, and S. phyteumoides Verdcourt. Herbarium collections rarely show the basal leaves, as the basal part is seldom collected. In the three abovementioned species, basal rosette leaves differ only slightly in size and shape from the cauline leaves. In S. heteromorpha, on the contrary, the basal leaves are markedly longer than the cauline ones. The type specimens of S. taylorii Verdcourt also have basal and cauline leaves, but the differences between the two leaf types are minor. THE MARUNGU HIGH PLATEAU The Marungu high plateau is situated southwest of Lake Tanganyika in D.R. Congo. The name of the plateau is derived from the word ‘‘dilungu,’’ which signifies ‘‘herbaceous plateau’’ (Verbeken, 1954). The name refers to a main feature of the environment, the absence of tree growth in the more elevated areas. NOVON 16: 231–234. PUBLISHED ON 26 JULY 2006. 232 Novon Very little detail is known, however, about the vegetation and environmental conditions of the region. Floristically, too, the area remains underexplored. Duvigneaud (1952) included the plateau in the ‘‘district des plateaux Katangais,’’ which also comprised the Biano, Kibara, and Kundelungu plateaus. Later, he placed the Marungu plateau in a district of its own because the vegetation shows several East African elements not found on the other Katangan plateaus (Duvigneaud, 1958). Most subsequent authors followed his opinion. The Marungu region reaches altitudes up to 2460 m (mont Lusale) and is mainly covered by savannahs (Lisowski et al., 1971). The vegetation of the savannahs is composed of many species of Cyperaceae and Poaceae, along with geoxylic herbs. During the dry season, other plants, such as Helichrysum Miller species (Asteraceae), may develop (Duvigneaud, 1958; Lisowski et al., 1971). White (1976) pointed out that the main factor accounting for the absence of trees is the waterlogged soils of the plateaus, rather than the presence of sporadic frost periods or temporal burning. The Marungu plateau is isolated from the other highland areas and thus forms an island of very peculiar environmental and edaphic conditions. As a consequence, the Marungu plateau might house a large number of endemic taxa, as observed on the other Katangan plateaus (Lisowski et al., 1971; Malaisse et al., 1995; Geerinck et al., 1996; Dessein et al., 2003). brescent; apex acute; base gradually narrowed; leaf margins somewhat thickened, beset with short stiff trichomes or scabrous; midvein somewhat prominent, densely pubescent toward the base underneath, sparsely pubescent above, with indistinct secondary and tertiary veins. Stipules fimbriate; stipule base 4– 18 mm long, beset with short appressed trichomes, often with stalked colleters in between the fimbriae; fimbriae 3 to 6, up to 6(212) mm long, ciliate. Flowers sessile in many-flowered capitula; inflorescences terminal, composed of several condensed flowering nodes each with a pair of subtending leaves, up to 3.5 cm wide in flowering stage; bracts stipuliform with numerous setae 3–6 mm long. Calyx tube ca. 0.5 mm high; lobes 2 or 3 (rarely no distinct lobes visible), narrowly triangular or leaf-like, often unequal, 2–8 mm long, beset with long hyaline trichomes, sometimes with numerous setae in between the lobes. Corolla blue; tube funnel-shaped, 6– 8.5 mm long, glabrous or sparsely pubescent outside, with a trichome ring around or below its middle inside; lobes triangular, 4–6 mm long, 2–2.5 mm wide at the base, pubescent outside, glabrous inside; anthers narrowly elliptic in outline, 1.5–2 mm long, exserted; filaments 1–2 mm long. Pollen 14–17zonocolporate, oblate to suboblate; equatorial diameter 67–83 mm; polar outline circular and somewhat lobed; ectocolpi relatively long; endoaperture a broad endocingulum; tectum perforate to microreticulate; microspines uniformly present; inner nexine surface granular with endocracks. Ovary ellipsoid to narrowly ellipsoid, 3–4.5 mm long, pubescent in the upper part; style 9–12 mm long, exserted; stigma shortly 2-lobed, ca. 1 mm wide; nectary disc bipartite. Capsule and mature seeds unknown; young seeds show the initiation of a basal elaiosome. TAXONOMY Spermacoce heteromorpha Dessein, sp. nov. TYPE: D.R. Congo. Katanga: plateau des Marungu, Kibobwa, 15 Feb. 1970, S. Lisowski, F. Malaisse & J.-J. Symoens 9696 (holotype, POZG; photos, BR, K, LV, MO, P). Figure 1. Similis Spermacocae taylorii a qua inflorescentiis terminalibus et compactis, antheris vix exsertis et caulibus pubescentibus differt. Praeterea bene distincta habitu heterophyllo manifesto, cum foliis basalibus duplo longioribus quam illis caulinis. Robust, erect herb with few stems from a woody perennial base with woody taproot; stems 45–55 cm tall, strictly erect, with short branches in the upper part bearing the inflorescences, densely covered with short, stiff, often ascending trichomes. Plants heterophyllous, with long leaves at the base and shorter cauline leaves. Leaves decussate, sessile, fused with the stipule base; blades of basal leaves narrowly elliptic to linear, (3–)11–22 6 0.7–2.2 cm; cauline leaves narrowly elliptic, (2–)5–10 6 0.8–1.7 cm, young leaves often densely covered with short stiff trichomes above and underneath, older leaves gla- Distribution, habitat, and phenology. Endemic to the northern part of the Zambezian regional centre of endemism: only known from two collections from the Marungu high plateau (Katanga province, D.R. Congo) in grassland at 1800–1900 m elevation. Flowering specimens were collected in February. Affinities with other species. Spermacoce heteromorpha is most similar to S. taylorii, a narrow endemic from the Songea district in Tanzania. The habit resemblance is especially striking: a woody base from which a few erect stems arise. Furthermore, S. taylorii shows a tendency toward the same type of heterophylly, much weaker, however, than in S. heteromorpha. Inflorescence and floral morphology clearly separate the two species. Whereas the flowers of S. heteromorpha are arranged in many-flowered terminal capitula, those of S. taylorii are in clusters at the Volume 16, Number 2 2006 Dessein et al. Spermacoce heteromorpha (Rubiaceae) 233 Figure 1. Spermacoce heteromorpha Dessein. —A. Habit. —B. Detail of stem. —C. Inflorescence. —D, D’. Flower buds showing variability of calyx. —E. Corolla, stamens, and style. —F. Open corolla showing stamens and a ring of trichomes. A. Lisowski, Malaisse & Symoens 9696 (POZG); B–F. Lisowski, Malaisse & Symoens 10061 (POZG). nodes along the stem, from which the upper 4 or 5 run together to form a more congested cone-like inflorescence. The corolla tubes are similar, but the corolla lobes are, based on Verdcourt’s (1976) measurements, much longer in S. taylorii (10– 11 mm vs. 4–6 mm). The anthers of S. heteromorpha are only exserted for 1–2 mm, while those of S. taylorii are exserted for more than 5 mm. Further evidence for the separation of the two species is found in the characteristics of the external indumentum: Spermacoce taylorii is almost entirely glabrous, whereas S. heteromorpha is densely covered with trichomes on almost all organs. Spermacoce perennis, collected from the northeastern part of Zambia, also has a similar habit. Spermacoce perennis lacks, however, some very characteristic features of S. heteromorpha: heterophylly is usually absent or, if present, the basal leaves are shorter than the cauline 234 Novon ones; the inflorescences are both terminal and axillary; the cauline leaves are much narrower; and secondary nerves are invisible. ———. 1958. Etudes sur la végétation du Katanga et de ses sols métallifères. Bull. Soc. Roy. Bot. Belgique 90: 127–286. Geerinck, D., F. Malaisse & M. Schaijes. 1996. Orchidaceae du district phytogéographique du Haut-Katanga (Zaı̈re): Biodiversité et endémisme. Pp. 795–801 in L. J. G. van der Maesen, X. M. van der Burgt & J. M. van Medenbach de Rooy (editors), The Biodiversity of African Plants: Proceedings of the XIVth AETFAT Congress. Kluwer Academic Publishers, Dordrecht. Harwood, R. & S. Dessein. 2005. Australian Spermacoce (Rubiaceae: Spermacoceae). I. Northern Territory. Austral. Syst. Bot. 18: 297–365. Lisowski, S., F. Malaisse & J. J. Symoens. 1971. Une flore des hauts plateaux du Katanga. Mitt. Bot. Staatssamml. München 10: 51–56. Malaisse, F., J. M. Lecron & M. Schaijes. 1995. Remarques à propos du genre Monadenium Pax (Euphorbiaceae), en particulier concernant les espèces de la région zambézienne. Bull. Séances Acad. Roy. Sci. Outre Mer. 40: 389–418. Robbrecht, E. 1988. Tropical woody Rubiaceae. Opera Bot. Belg. 1. National Botanic Garden of Belgium, Meise. Verbeken, A. 1954. Contribution à la géographie historique du Katanga et de régions voisines. Koninklijk Belgisch Koloniaal Instituut, Brussel. Verdcourt, B. 1976. Rubiaceae (part 1): Spermacoce. Pp. 339–374 in R. M. Polhill (editor), Flora of Tropical East Africa. Crown Agents for Oversea Governments and Administrations, London. White, F. 1976. The underground forests of Africa: A preliminary review. Gard. Bull. Singapore. XXIX: 57–71. Paratype. D.R. CONGO. Katanga: plateau des Marungu, au pied du mont Kibobwa, au-dessus du village Kibobwa, steppe au bord d’une petite rivière, 29u429E 7u319S, 1900 m, 19 Feb. 1970, S. Lisowski, F. Malaisse & J.-J. Symoens 10061 (POZG; photos, BR, K, LV, P). Acknowledgments. The authors are indebted to Anja Vandeperre for the illustration and to the curator of POZG for specimens loaned. This study was supported by grants from the Research Council of the K.U. Leuven (OT/01/25) and the Research Foundation Flanders (1.5.069.02). Fieldwork in Zambia was supported by the ‘‘Stichting tot bevordering van het wetenschappelijk onderzoek in Afrika.’’ Literature Cited Dessein, S., S. Jansen, E. Robbrecht & E. Smets. 2002. A new species of Spermacoce (Rubiaceae) from the Manika high plateau (Katanga; R.D. Congo). Nordic J. Bot. 22: 513–523. ———, S. Ntore, E. Robbrecht & E. Smets. 2003. Pollen and seeds reveal that Spermacoce thymoidea s.l. (African Rubiaceae, Spermacoceae) represents three endemic or disjunct species from the Zambezian high plateaus. Syst. Bot. 28: 130–144. Duvigneaud, P. 1952. La flore et la végétation du Congo méridional. Lejeunia 16: 95–124.