Acosmium Schott is a Neotropical genus of ca. 17 species of trees with non-papilionoid, actinomorphic flowers. it has been included in the genistoid clade (Leguminosae, Papilionoideae) in recent phylogenetic analyses. A morphology-based cladistic analysis was performed to test the currently assumed monophyly of Acosmium, assess the validity of the infrageneric classification of Yakovlev, and detect synapomorphies and other diagnostic characters in Acosmium and related taxa. Thirty-four species representing ten genera of subfamily Papilionoideae were included in the analysis: all accepted species of the four sections of Acosmium together with species of Bowdichia, Clathrotropis, Diplotropis, Bolusanthus, Cadia, Poecilanthe, Cyclolobium, and Ormosia; two species of Luetzelburgia were selected as outgroups. The results do not support the monophyly of Acosmium; the species of this genus fall into three distinct, not closely related clades that correspond to the sections of Acosmium established by Yakoviev except for sect. Mesitis that merges into sect. Leptolobium. We propose: (1) recognizing a narrowly circumscribed genus Acosmium; (2) reinstating the generic name Leptolobium Vogel, encompassing sections Leptolobium and Mesitis; and (3) segregating A. praeclarum (Sandwith) Yakovlev into a new genus, Guianodendron. The phylogenetic relevance of some new or neglected characters, especially from bud architecture, seed, and seedling morphology is emphasized.56243945
