We present a taxonomic revision of the Cohniella species occurring south of the Amazon River in South America. In this revision, we recognize a naturally occuring hybrid and six species, one of which is herein proposed as new, Cohniella caatingaensis, restricted to the Caatinga of northeastern Brazil. Furthermore, we clarify the specific circumscriptions and distribution range of C. binotii, C. cepula, and C. sprucei. Based on vegetative and floral morphology, we recognize two species groups, the C. jonesiana and the C. cepula complexes. Detailed taxonomic descriptions are given for all species, including short accounts of their distribution and ecology, diagnostic characters, variation range, taxonomic comments, and additional material examined. Relevant iconography is listed for each species. Additionally, a key and a table featuring diagnostic characters to distinguish between species are provided as well as distribution maps for each species-complex.