Generic delimitation in Apocyneae (Apocynaceae)

Apocyneae are a tribe of 24 genera and ca. 113 species that, with the exception of the temperate Apocynum species in North America and Eurasia, are all woody vines endemic to tropical and subtropical Asia and Australasia. Generic concepts have been in flux through most of the history of the taxa now grouped in Apocyneae and have been only partially clarified in previously published molecular phylogenetic studies. Expanded taxon and character sampling permitted a phylogenetic analysis based on gene sequences from four chloroplast and three nuclear loci of 23 of 24 currently recognized genera, and 23 morphological characters scored for all 24 genera. The resulting topology supports the expansion of Micrechites to include the monotypic Vallariopsis, united by the shared presence of unusual polyporate pollen, and Urceola to include Parameria and Aganonerion, united by the shared presence of acarodomatia and pubescent seeds. The required combinations are made. Ixodonerium is placed as sister to Papuechites, supported by the synapomorphic presence of a corolline corona. Monophyly of Epigynum is supported for the first time, based primarily on evidence from the nuclear Leafy intron; no unambiguously optimized morphological synapomorphies are identified. Baharuia, included based on morphology only, is placed as sister to or nested within Urceola s.l., supported by the synapomorphic presence of acarodomatia. The subtribal classification is modified to reflect our current understanding of phylogeny: Baharuia is transferred to Urceolinae, Micrechites and Amalocalyx are transferred to Chonemorphinae, and Streptoechites is treated as subtribe incertae sedis.