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

Abstract

Stylosanthes Sw. is a pantropical genus primarily distributed throughout the Americas, with the Brazilian Cerrado serving as its principal center of diversity. Many of its species hold significant economic potential and are widely utilized as fodder for cattle. Systematic examinations involving both 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 S. 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. Furthermore, a neotype for S. nunoi Brandão is designated due to the loss of the holotype. Stylosanthes pohliana Taub. is reinstated as an accepted species, and a novel species within the genus is described. X-ray imaging of leaflets emerges as a valuable tool for taxonomic discrimination. This comprehensive study not only presents nomenclatural modifications but also provides illustrations, comments on diagnostic characteristics, distribution maps, and preliminary IUCN conservation assessments. Additionally, a novel discovery is introduced with the recognition of an elaiosome in the fruits of S. guianensis, constituting a noteworthy addition to the tribe Dalbergieae.