Systematics of Gonolobus and the Gonolobinae (Apocynaceae, Asclepiadoideae): Circumscription based on evidence from molecules and morphology; new species and combinations; typification, revision, and conservation in the West Indies

Gonolobus Michx. (Apocynaceae, Asclepiadoideae) is a New World genus comprising an estimated 100–150 species. The degree of variation in estimated species numbers is largely the result of still poorly known tropical taxa and differences regarding generic limits. Characters historically used to delimit genera such as Gonolobus within Gonolobinae—such as laminar dorsal anther appendages and various follicle morphologies—have been controversial and their evolution remains unknown, not having been explored in a phylogenetic framework. The primary objectives of the current research were to (1) test the monophyly of Gonolobus in the context of a phylogeny of New World Asclepiadeae and (2) explore the evolution of laminar dorsal anther appendages and winged follicles with respect to their potential utility in generic circumscription. Secondary objectives were to revise a tractable monophyletic group as borne out by the phylogenetic analyses and to provide typifications and new combinations as appropriate for Gonolobinae in the West Indies (ca. 50 spp.). Evidence from the chloroplast ( trnL-F, rps16) and nuclear genomes (Leafy) presented here supports the monophyly of both the subtribe and the genus Gonolobus in a narrow or broad sense. A transversion in the trnL-F spacer is shown synapomorphic for Gonolobus s.s. Two indels in Leafy, as well as winged follicles, are shown synapomorphic for Gonolobus s.l. Several earlier subgeneric circumscriptions in Matelea, including Ibatia, Heliostemma, Pachystelma, and Ptycanthera, are not monophyletic. Considering the support for a monophyletic Gonolobus s.s., recent taxonomic changes in West Indian taxa, and that several species have been published from the area since the last comprehensive treatment over a hundred years ago, a revision of the genus in the West Indies seemed appropriate and is provided. An index of names and typifications for Gonolobinae in the West Indies is also provided, including numerous lecto- and neotypifications. Twelve new species are described for the West Indies (5 Gonolobus spp., 5 Matelea spp.) and South America (2 Matelea spp.).