Molecular and Morphological Analysis Supports the Separation ofRobrichiaas a Genus Distinct fromEnterolobium(Leguminosae: Caesalpinioideae: Mimosoid Clade)

Abstract

Abstract—As currently circumscribed, the legume genusEnterolobiumcomprises 11 species in two sections:E.sect.EnterolobiumandE.sect.Robrichia, with an overall distribution from Mexico to Argentina and a centre of diversity in Amazonia. In the absence of the characteristic indehiscent fruits,Enterolobiumis difficult to distinguish from other genera in the ingoid clade, includingAlbiziasensu lato,Samanea, andCathormion. Previous phylogenetic studies which have includedEnterolobiumhave sampled few species of the genus, leaving questions about its monophyly and interspecific relationships. Here we evaluate the circumscription ofEnterolobiumand its two infrageneric taxa, their phylogenetic placement in the ingoid clade, and interspecific relationships within the two sections of the genus. Our study includes allEnterolobiumspecies, and analyses of nuclear (ITS and ETS) and plastid (trnD-TandtrnL-F) molecular regions, and morphology. Bayesian inference, maximum parsimony, and maximum likelihood analyses show thatEnterolobium, as presently circumscribed, is not monophyletic. The genus is divided into two well-supported independent clades, corresponding to the two previously recognized sections; one of them is sister to the genusLeucochloronand is here raised to generic rank as the genusRobrichia, with three species,Robrichia glaziovii,Robrichia oldemaniiandRobrichia schomburgkii. The genusEnterolobiumconsequently now comprises eight species and is more closely related to a clade composed ofAlbiziaandFalcataria. This new arrangement is reinforced by morphological synapomorphies recovered by ancestral character state reconstructions. Indumentum type, the number of pinnae pairs per bipinnate leaf and leaflet pairs per pinna, inflorescence type, and fruit shape characterizeRobrichia, while the recognition ofEnterolobiumremains based on fruit traits. We also provide the formal lectotypifications forE. contortisiliquum,E. cyclocarpum,E. gummiferum,E. maximum,E. monjollo, andR. schomburgkii.