Senna sect. Chamaefistula (DC. ex Collad.) H. S. Irwin & Barneby ser. Spinescentes H. S. Irwin & Barneby is restricted to the Neotropical region and has species distributed predominantly in the lowland forest of Amazonia. These species are morphologically distinguished by their scandent or viny habit, stipular thorns, and laterally compressed fruits with seeds parallel to fruit valves. Previous taxonomic treatments have recognized only two formally described species and one variety; nevertheless, they served as a baseline for a more comprehensive study. Based on the analysis of many specimens housed in herbaria and on fieldwork, we recognize five species belonging to Senna ser. Spinescentes including two newly described species, one from the Brazilian Amazon, S. manaosa A. Lima, Bortoluzzi & V. F. Mansano, and the other from the Bolivian Yungas, S. yungas A. Lima, Bortoluzzi & V. F. Mansano. We also recognize S. schultesiana (H. S. Irwin & Barneby) A. Lima & V. F. Mansano as a morphologically distinct species rather than a variety of S. spinescens (Hoffmanns. ex Vogel) H. S. Irwin & Barneby, and we propose a lectotypification for S. longiglandulosa (Benth.) H. S. Irwin & Barneby. We provide an identification key, morphological descriptions, taxonomic notes, illustrations, preliminary conservation assessments, and habitat and phenology data for each species of the series.