Morphological analyses support taxonomic updates in Brazilian species of Stylosanthes Sw. (Papilionoideae, Leguminosae)

Stylosanthes Sw. is a pantropical genus primarily distributed throughout the Americas, with the Brazilian Cerrado serving as its principal center of diversity. Stylosanthes species have a subshrub habit, trifoliolate leaves, amplexicaul stipules, and loments with a rostrum derived from the remnant style. Many of its species hold significant economic potential and are widely used as cattle fodder. Systematic examinations involving morphology and nomenclature have highlighted the imperative need for taxonomic updates in select species. Given the observed morphological and ecological differences, a taxonomic reevaluation of Stylosanthes guianensis (Aubl.) Sw. was deemed necessary, leading to the elevation of its varieties to the species level. The taxonomic changes include the new combinations S. microcephala (M.B. Ferreira & Sousa Costa) Gissi, S. pauciflora (M.B. Ferreira & Sousa Costa) Gissi, and S. pubescens (Pilger) Gissi, as well as the reinstatement of Stylosanthes pohliana Taub. as an accepted species. X-ray imaging of leaflets emerges as a valuable tool for taxonomic discrimination. Additionally, a novel discovery is presented with the recognition of an elaiosome in the fruits of S. guianensis, constituting a noteworthy addition to the tribe Dalbergieae. A novel species within the genus is described, and a neotype for S. nunoi Brandão is designated due to the loss of the holotype. This study not only presents nomenclatural modifications but also provides illustrations, comments on diagnostic characteristics, distribution maps, and preliminary IUCN conservation assessments.