Phylogenetics of neotropical Platymiscium (Leguminosae: Dalbergieae): systematics, divergence times, and biogeography inferred from nuclear ribosomal and plastid DNA sequence data

Abstract

Platymiscium is a neotropical legume genus of forest trees in the Pterocarpus clade of the pantropical "dalbergioid" clade. It comprises 19 species (29 taxa), distributed from Mexico to southern Brazil. This study presents a molecular phylogenetic analysis of Platymiscium and allies inferred from nuclear ribosomal (nrITS) and plastid (trnL, trnL-F and matK) DNA sequence data using parsimony and Bayesian methods. Divergence times are estimated using a Bayesian method assuming a relaxed molecular clock (multidivtime). Within the Pterocarpus clade, new sister relationships are recovered: Pterocarpus + Etaballia, Inocarpus + Tipuana and Paramachaerium + Maraniona. Our results support monophyly of Platymiscium, which is resolved into three major clades, each with distinct geographic ranges and ecological preferences. Diversification in Platymiscium has been driven by habitat fragmentation, invasion of novel geographic regions, and ecological diversification, revealing general patterns of diversification in the neotropics. We hypothesize that Platymiscium arose in dry habitats of South America and radiated northward. The Amazon basin was invaded twice both within the last 5.6 My and Central America twice before the closure of the Isthmus of Panama. Divergence times of the P. pubescens complex, restricted to seasonally dry tropical forests of South America, support pre-Pleistocene divergence in this biome.