The genus Collaea belongs to tribe Diocleae (Leguminosae subfamily Papilionoideae) and includes eight species from South America. A new species from South Brazil was discovered during a taxonomic revision of the genus and is formally described as Collaea caerulea. This species is found in a small area of Santa Catarina State, near the border with Paraná State, in regenerating secondary forests. It can be differentiated from other species from South Brazil by the combination of narrowly elliptical leaflets with an acuminate apex and bluish-lilac to bluish petals. The region where the species was discovered has only been recently explored by botanists and its natural vegetation is currently highly fragmented. Considering these factors, we propose that this species be classified as critically endangered. Here, we present a morphological description, geographical distribution, preliminary conservation assessment, and illustrations of the new species. We have also included an identification key for all Brazilian species of the genus.
