Phylogeny of Marsdenieae (Apocynaceae, Asclepiadoideae) based on chloroplast and nuclear loci, with a conspectus of the genera

Abstract

AbstractA densely sampled molecular phylogeny of the pantropical, predominantly forest‐dwelling tribe Marsdenieae (Apocynaceae) is presented, including almost a quarter of the ca. 740 species. Sampling focused on resolving the circumscription of Marsdenia, which ranges from Marsdenia sensu Bullock with less than 10 Asian species closely related to the type, M. tinctoria, to Marsdenia sensu Forster, with ca. 300 species distributed throughout the range of the tribe, encompassing the genera Cionura, Dregea, Gongronema, Gymnema, Leichhardtia, Stephanotis, and Wattakaka as synonyms. All analyses resolve two well‐supported clades: an Asia‐Pacific Clade that includes the large epiphytic Dischidia‐Hoya alliance and a number of Marsdenia species, among them the type M. tinctoria, and a Cosmopolitan Clade that includes most of the rest of Marsdenieae with several moderately to well‐supported subclades that span the entire geographic range of Marsdenieae. The position of two small genera, Rhyssolobium (southern Africa) and Sicyocarpus (Madagascar), is ambiguous. Given this topology, a monophyletic Marsdenia s.l. would subsume all species of Marsdenieae. Instead, we propose a classification that maintains Dischidia and Hoya as distinct genera. We revise generic circumscriptions, reducing Marsdenia s.str. to a small clade of Asian species. Two new genera, Gongreos gen. nov. and Gongronemopsis gen. nov., are described, with two and nine species, respectively. A total of twenty‐six new combinations, one new name, and six new synonyms are proposed. Three neotypes and eleven lectotypes are selected, and one 2nd step lectotypification is carried out. Diagnostic morphological characters for identified clades are discussed. Biogeographic analysis retrieves tropical Asia as most likely ancestral area for Marsdenieae, with widespread tropical Asia‐Africa almost equally likely. The first‐branching lineages in both major clades are tropical Asian; the Asia‐Pacific Clade comprises a sizeable radiation in the Pacific area, with two dispersals from Australia to New Caledonia. The Cosmopolitan Clade comprises several genera (Gongronemopsis, Gymnema, Stephanotis, Telosma) widespread in Africa and tropical Asia, and some also in Madagascar, and the New World genus Ruehssia.