A detailed investigation of the Pterocarpus clade (Leguminosae: Dalbergieae): Etaballia with radially symmetrical flowers is nested within the papilionoid-flowered Pterocarpus

The pantropical genus Pterocarpus (Leguminosae: Dalbergieae) with papilionoid flowers, and allied genera in the Pterocarpus clade were sampled for the five molecular markers ITS2, trnL-F, ndhF-rpL32, matK, and rbcL, as part of our ongoing systematic studies in the clade. For wider analyses of the Pterocarpus clade the remaining 14 members of this clade were also sampled for matK. Phylogenetic analyses were performed under the maximum likelihood criterion (ML) and Bayesian criteria. In the five-marker analysis of the core Pterocarpus clade (including 106 accessions) two robustly supported clades were resolved. The first clade includes Centrolobium, Etaballia, Inocarpus, Maraniona, Paramachaerium, Pterocarpus, Ramorinoa, and Tipuana. The second includes all species of Pterocarpus (except P. acapulcensis), Etaballia with radially symmetric flowers, and Paramachaerium. Paramachaerium is placed as sister to the several Pterocarpus species from South America, while Etaballia is resolved within the clade containing the African and Asian species of Pterocarpus. The wider sampled matK data set includes 199 accessions. Discolobium and Riedeliella are recovered as sister to the remaining Pterocarpus clade. Platymiscium is strongly supported as sister to the rest of the members of the clade, and Pterocarpus acapulcensis is also here resolved in a separate lineage from the remaining Pterocarpus accessions. We used the phylogenies to investigate patterns of floral evolvability in the Pterocarpus clade, which include four genera with actinomorphic flowers (Acosmium s.s., Etaballia, Inocarpus and Riedelliela). Our results reinforce the hypothesis that flower evolvability is high in early-branching legume lineages, and that actinomorphy has evolved independently four times in the Pterocarpus clade. In light of our results, the taxonomic status of the monospecific genus Etaballia dubia Benth. was revisited, and the species is synonymized as belonging to Pterocarpus, under the name Pterocarpus dubius Spreng., published in 1827, but hiding in synonymy for nearly two centuries.