Revisiting the taxonomy of Dioclea and related genera (Leguminosae, Papilionoideae), with new generic circumscriptions

Abstract

The Dioclea clade comprises four genera and aproximately 60 species of the tribe Diocleae: Cleobulia (4 species), Cymbosema (1), Dioclea (ca. 50), Luzonia (1) and Macropsychanthus (3–4). Dioclea has been demonstrated to be a non-monophyletic genus, but low sampling in previous phylogenetic studies hampered the adoption of new taxonomic arrangements. We carried out densely sampled phylogenetic analyses of the Dioclea clade using molecular markers that had performed well in previous studies: the ITS and ETS nuclear ribosomal regions and the plastid trnK/matK. Our results support the maintenance of the genera Cleobulia and Cymbosema with their current circumscriptions, but confirmed the polyphyly of Dioclea, with its species falling into three different positions: (1) the puzzling species, Dioclea paniculata, was highly supported as a member of the Galactia clade; (2) Dioclea subg. Dioclea appeared as sister to a clade composed of Cleobulia and Cymbosema; and (3) the species of Dioclea subgenera Pachylobium and Platylobium composed a paraphyletic grade nesting the genera Luzonia and Macropsychanthus. We thus propose that the circumscription of Dioclea should be restricted to Dioclea subg. Dioclea, with 13 species and that the limits of Macropsychanthus should be widened to include the genus Luzonia, as well as the Dioclea subgenera Pachylobium and Platylobium, with 46 species. Taxonomic summaries, new combinations and synonyms are presented for all genera of the Dioclea clade. Cleobulia and Cymbosema were retained in their original circumscriptions. We presented an illustrated taxonomic conspectus of all genera of the Dioclea clade including 44 new combinations, one new name, ten new synonyms, two re-established holotypes, 38 lectotypes, two epitypes and one neotype.