Notes on Secamonoideae (Apocynaceae) in Africa Jens KLACKENBERG Naturhistoriska riksmuseet, Sektionen för fanerogambotanik, Box 50007, SE-104 05 Stockholm, Sweden. [email protected] ABSTRACT The African taxa that have been referred to Toxocarpus (Apocynaceae, Secamonoideae) are revised. All three species, including one species some- times placed in a monotypic genus, Rhynchostigma, are transferred to Secamone. The following recombinations are made: Secamone brevipes (Benth.) Klack., S. letouzeana (H. Huber) Klack. and S. racemosa (Benth.) Klack. In addition a fourth species is described as new and given the name S. goyderi Klack. Keys to the genera of subfamily Secamonoideae from conti- KEY WORDS nental Africa and Madagascar and to the continental African species of genus Apocynaceae, Secamonoideae, Secamone are given. Descriptions, distributions and drawings of the four Africa. species added to Secamone are given. RÉSUMÉ Notes sur les Secamonoideae (Apocynaceae) d’Afrique. Les taxons africains qui ont été rattachés au genre Toxocarpus (Apocynaceae, Secamonoideae) sont revisés. Les trois espèces, y compris celle placée dans le genre monotypique Rhynchostigma, sont transférées dans le genre Secamone. Les combinaisons suivantes sont établies : Secamone brevipes (Benth.) Klack., S. letouzeana (H. Huber) Klack. et S. racemosa (Benth.) Klack. De plus, une quatrième espèce, reconnue comme nouvelle, S. goyderi Klack., est décrite. Des clés de détermination des genres de la sous-famille des Secamonoideae en MOTS CLÉS Afrique continentale et Madagascar et des espèces de Secamone d’Afrique Apocynaceae, Secamonoideae, continentale sont présentées. Les descriptions, distributions et illustrations de Afrique. ces quatre espèces rattachées au genre Secamone sont données. ADANSONIA, sér. 3 • 2001 • 23 (2) : 317-335 © Publications Scientifiques du Muséum national d’Histoire naturelle, Paris. 317 Klackenberg J. INTRODUCTION Socotra (GOYDER 1992) and in Asia at present two species are recognized (KLACKENBERG Subfamily Secamonoideae is characterized 1992b). by having four pollinia per corpusculum, not two as in Asclepiadoideae, and by not lacking a corpusculum and instead furnished with a MATERIAL AND METHODS spoon-like pollen carrier as in Periplocoideae. In a recent classification of Apocynaceae s.l., This study is based on herbarium material ENDRESS & BRUYNS (2000) accepted nine from the following herbaria (abbreviations genera in Secamonoideae Endl., viz. according to HOLMGREN et al. 1990): A, B, BM, Calyptranthera Klack., Genianthus Hook f., BR, G, GH, K, L, MO, NY, P, US and Z. Goniostemma Wight, Pervillaea Decne., All specimens cited have been studied if not Rhynchostigma Benth., Secamone R. Br., otherwise stated. Secamonopsis Jum., Toxocarpus Wight & Arn. Asclepiadaceae are included in Apocynaceae and Trichosandra Decne. Six of those are s.l. and the classification of the family follows found in Madagascar and continental Africa, ENDRESS & BRUYNS (2000), i.e. the former fam- i.e. Calyptranthera, Pervillaea, Rhynchostigma, ily Asclepiadaceae is subdivided into three sub- Secamone, Secamonopsis and Toxocarpus. families: Periplocoideae, Secamonoideae and Calyptranthera, Pervillaea and Secamonopsis Asclepiadoideae. are endemic to Madagascar, while Secamone Measurements of floral parts were made and Toxocarpus are considered to be wide- on boiled material, of vegetative parts and spread in Africa, India and Southeast Asia, fruits on dry material. The measurements of and the monotypic Rhynchostigma to be an the gynostegium are in accordance with ear- endemic to central tropical Africa. In this lier studies of Secamone in Madagascar and paper, however, it will be shown that African Asia (see KLACKENBERG 1992a). The style species of Toxocarpus and Rhynchostigma are head in Secamone is situated directly on the better included in Secamone. This means that ovary. It has a broader “basal portion” with subfamily Secamonoideae is represented in the stigmatic area just below the top and a continental Africa by the single genus narrower (at least at base) “apical portion” Secamone. (= “broader basal part” and “narrower apical Secamone consists of suffrutescent twiners or part” of “stigma head” in KLACKENBERG small scrambling herbs with usually white to 1992a,b). yellow small flowers. It is distributed in Africa The species concept used in this revision from Cape Province in the south to Senegal, conforms to KLACKENBERG (1992b). Republic of Central Africa and northern The drawings were made from herbarium Somalia in the north. It also occurs on Bioko material. Island (Fernando Poo) in the Bay of Guinea. The genus is widely distributed in Madagascar and is also present on several smaller islands in TAXONOMIC ORIENTATION AND NOTES the Indian Ocean, i.e. Mauritius, La Réunion, ON MORPHOLOGY Rodrigues, Seychelles, Socotra, Zanzibar, Pemba and Comoros. In Asia it is found in Sri The subfamily Secamonoideae is characterized Lanka and southern India, and from southern by having four pollinia per corpusculum, not China in the northwest through Southeast Asia two as in Asclepiadoideae. Four pollinia, how- to eastern Australia and New Caledonia. On ever, is considered a primitive character and the African mainland 19 species are recognized consequently not possible to use to characterize (GOYDER 1992 and this paper), in Madagascar this subfamily (KLACKENBERG 1992a). and adjacent islands 69 species (KLACKENBERG Recognition of the Secamonoideae as a separate 1992a, 1997b, 1998, 2000a,b,c), one on subfamily was recently discussed by ENDRESS & 318 ADANSONIA, sér. 3 • 2001 • 23 (2) Secamonoideae (Apocynaceae) in Africa BRUYNS (2000). However, no apomorphies for material, but blurred when studying African and this taxon were presented. The pollinia of Malagasy Secamonoideae (KLACKENBERG Secamonoideae differ from those in 1992a). The plasticity of the corona structure in Asclepiadoideae in that they are composed of Apocynaceae was also discussed by WOODSON. tetrads held together by cross-wall fusion, with- He concluded that “authors ... seem not to have out an outer wall enclosing the pollinium. Also understood what a versatile feature this organ is” in this character Secamonoideae are primitive (WOODSON 1941), and discarded the variation and similar to those few genera of Periplocoideae in corona morphology as a character to be used that have pollinia. The apomorphic character, at generic level. This is surprising taken into i.e. pollinia with individual pollen grains and account the delicate function carried out by the the whole structure covered by a thick wall, is corona in pollination. A variable nature of the found in the Asclepiadoideae. The subfamily is corona lobe morphology, however, is corrobo- easily recognized as presently circumscribed, rated if studying the shape of the corona in rela- however, by these plesiomorphies and by the tion to a phylogeny based on molecular data. soft semi-ellipsoid corpuscules which are U- From the cladogram presented by CIVEYREL shaped in cross section. Although it is difficult (1996, fig. 41) it can be seen that species with to point at morphological apomorphies to char- considerable differences in corona morphology acterize Secamonoideae, recent molecular stud- show up as closely related species in a repeated ies (gene matK) of Apocynaceae (by CIVEYREL pattern within the genus. For example, S. falcata 1996; CIVEYREL et al. 1998) nevertheless show Klack. with distinctly falcate lobes and S. buxi- this subfamily to be monophyletic. Some genera folia Decne. with dorsiventrally compressed within the subfamily seem to be monophyletic. rather straight lobes, group together. This is true for the Malagasy endemics Furthermore, S. sparsiflora Klack. (dorsiventrally Secamonopsis, Pervillaea and Calyptranthera, but compressed lobes) forms a clade with S. unciata might also to be the case for the widely distrib- Choux (slightly laterally compressed lobes). uted Secamone (CIVEYREL 1996; CIVEYREL et al. Secamone ecoronata Klack., which lacks corona 1998; KLACKENBERG 1996a, 1997a). No species lobes, is related to S. minutifolia Choux, which of Toxocarpus nor Genianthus were included in has well developed dorsiventrally compressed these analyses, however, and much data still is corona lobes. Consequently, the shape of the lacking in order to sort out monophyletic staminal corona seems to be variable and of lim- groups within the subfamily. Nevertheless, ited taxonomic value at generic level in this African Secamone seem to form a monophyletic taxon group. group together with the Malagasy species of the GOYDER (1992) recognized 16 species in a genus (CIVEYREL 1996; CIVEYREL et al. 1998) revision of continental African Secamone. Because and, according to the analyses of CIVEYREL of the uncertain boundaries within the subfamily, (1996, fig. 41), are probably even nested within three species which traditionally have been placed the Malagasy taxa. Only one African species in Toxocarpus and Rhynchostigma due to their dor- (S. parvifolia (Oliv.) Bullock), however, has been siventrally flattened corona lobes, were excluded. analysed so far. These are the taxa primarily dealt with in this The generic delimitation of Secamone in rela- paper. These three species together with the new tion to Toxocarpus has been discussed several species here described, show many diagnostic times (DECAISNE 1844; BENTHAM 1876; characters inseparable from Malagasy Secamone SCHUMANN 1895; BROWN 1902; SCHLECHTER and, seen in a wider perspective, cannot be kept 1907, 1914;