A synopsis of Senna ser. Bacillares (Leguminosae, Caesalpinioideae, Cassieae) in Brazil, including a remarkable new species from Amazonia

Abstract

Senna (Leguminosae, Cassieae) comprises ca. 300 species mainly distributed throughout the Americas. Although the genus is speciose and taxonomically problematic, very few studies have addressed the systematics of Senna in recent years, and many taxonomic and nomenclatural issues remain unresolved. Senna sect. Chamaefistula ser. Bacillares is the most speciose of the American series of Senna and is the most problematic series in the genus. Based on fieldwork and extensive analysis of herbarium collections, we document the occurrence of 29 species of Senna ser. Bacillares in Brazil. This total includes Senna rionegrensis , which is newly described from Amazonia and distinguished by its short abaxial stamens. We provide a synopical treatment of the taxa of Senna ser. Bacillares occurring in Brazil, including identification keys, short morphological descriptions, taxonomic notes, and distributional and phenological data. This work contributes to the taxonomic knowledge of Senna ser. Bacillares in Brazil and serves as a baseline for our ongoing taxonomic revision.

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