Premise of research. The Neotropical endemic Macrolobium is one of the most species-rich genera (ca. 75 species) within subfamily Detarioideae (Fabaceae, alternatively Leguminosae). Two sections distinguished by floral morphology have been recognized in the past. Although morphologically diverse, species within the genus share several characters, including a single well-developed petal in adaxial position. However, previous analyses based on plastid markers have suggested that the genus is not monophyletic. We produce the most densely sampled molecular phylogeny of Macrolobium and test the monophyly of the genus and the two sections.

Methodology. We analyzed nucleotide sequence data from the nuclear ribosomal internal transcribed spacer (ITS) and plastid (matK, trnG) genomes using Bayesian and maximum likelihood analyses.

Pivotal results. The combined analysis retains Macrolobium as a monophyletic genus, with two well-supported subclades corresponding to the two recognized sections. Macrolobium pendulum is the only species placed in a section different from its taxonomic treatment. The relationships recovered with the plastid markers differ slightly from the combined and ITS analyses, but without significant support.

Conclusions. Macrolobium is shown to be a monophyletic genus and to contain two well-supported and morphologically defined sections with differing Amazonian and Andean/Central American distributions corresponding to the Gentry pattern. Species are also found to group partly according to habitat preferences and leaf morphology. Both sections contain groups of multijugate and unijugate species, and there appear to have been multiple shifts of this character.