Diversity and evolution of leaflet anatomical characters in the Pterocarpus clade (Fabaceae: Papilionoideae)

The Pterocarpus clade includes 23 genera previously attributed to different Fabaceae tribes. The recent rearrangements of many genera in the clade do not recognize morphological synapomorphies. This study aimed to identify new synapomorphies for the Pterocarpus clade, to identify characters supporting inter-generic relationships currently resolved only by molecular data and to identify diagnostic characters at the genus and species levels. Subterminal leaflets of the studied genera were selected and analyzed using light and scanning electron microscopy. Ancestral reconstruction was performed using morphological and anatomical characters of 16 genera of the Pterocarpus clade. The convex epidermal relief in the region of the main vein indicated the relationship among all genera of the group. Anchor-like multicellular trichomes are features shared by Brya and Cranocarpus, which are the sister group to the other genera of the clade. Subepidermal layers are features shared by the Centrolobium, Etaballia, Paramachaerium, Pterocarpus and Tipuana genera, and the sclerenchyma sheath in the leaflet margin is reported in the Discolobium, Riedeliella and Platymiscium genera. Bulbous based glandular trichomes and vesicular glandular trichomes are diagnostic at the species level in Centrolobium and Pterocarpus, respectively. The leaflet characters investigated can be useful for the taxonomic delimitation at both the genus and species levels of the Pterocarpus clade. Our dataset provides new synapomorphies, elucidates the inter-generic relationships and reinforces the phylogenetic classification of the Pterocarpus clade resolved by molecular data.