Phylogeny, niche modelling and morphology unveil a new lianescent species of Sigmoidotropis (Leguminosae, Papilionoideae) across rainforest enclaves within Brazilian dry vegetation

Abstract

The small Neotropical papilionoid legume genus Sigmoidotropis (nine species) has been described only relatively recently as the result of the taxonomic rearrangement of the genus Vigna (subtribe Phaseolinae), based on phylogenetic analyses of DNA sequence data. Here, we formally propose a new lianescent species of Sigmoidotropis that occurs disjunctly in enclaves of moist forest of mountainous regions surrounded by dry vegetation at three different localities in the Brazilian states of Bahia and Minas Gerais. Its phylogenetic position and morphological affinities with other genera of Phaseolinae were evaluated by Bayesian inference and maximum likelihood analyses, using sequence data from the nuclear ITS/5.8S and plastid trnK/matK. To better understand this new species’ widely disjunct distribution and a possible connection between its populations in the past, an environmental niche modelling (ENM) analysis was performed. The phylogenetic analyses revealed that Sigmoidotropis appears closest to the genera Ancistrotropis and Delgadoana, together forming the Sigmoid‐keel clade. The new species proposed here is strongly recovered within Sigmoidotropis, being most closely related to S. ekmaniana, S. elegans, and S. megatyla. The ENM indicated changes in the potential distribution of the new species over different climatic periods, with expansion during colder periods and contraction during warmer periods, leading to possible relictual populations in moist forest enclaves. A description of the new species Sigmoidotropis maculata is presented, along with illustrations, a distribution map, taxonomic comments, and conservation status assessment.