Taxonomic study of Senna section Chamaefistula series Bacillares (Fabaceae) in the Atlantic Forest north of the São Francisco River, Brazil, and nomenclatural updates

Senna section Chamaefistula series Bacillares (Benth.) H.S.Irwin & Barneby comprises ~50 Neotropical legume species occurring in both tropical and subtropical areas. Approximately 25 of those species occur in Brazil, with nine being endemic. This work provides a taxonomic study of Senna section Chamaefistula series Bacillares in the Atlantic Forest north of the São Francisco River in north-eastern Brazil, which is considered a global hotspot for biodiversity, contributing to understanding their taxonomy, diversity and distribution, as well as analysing morphological variations that have led to identification errors in the past. Fieldwork was conducted to make observations and collect fresh material; specimens from national and international herbaria were also examined. Senna section Chamaefistula series Bacillares is represented in the study area by nine species (of which four are endemic to Brazil), including S. pluribracteata F.S.Souto & R.T.Queiroz, a species recently described for the area. All species of the series known from the study area are described and illustrated and a key is provided. Additionally, four names were typified, with two lectotypes and two neotypes being designated here. The results have reinforced the importance of conducting floristic inventories for documenting new species and new occurrences.