A new species of Actinostemon (Euphorbiaceae) from Southern Bahia Atlantic Forest, Brazil.

Actinostemon (Euphorbiaceae, Hippomaneae) is a Neotropical genus, with a total of 16 species. Brazil stands out as its center of diversity with nine species, most from seasonal dry forests of the Atlantic Forest. Through the analysis of herbarium specimens, protologue and field collections, we present here a new species, Actinostemon sessilantherus, from southern Bahia. Actinostemon sessilantherus resembles A. concolor in its alternate, non pseudoverticillate leaves, coriaceous blades and cataphylls, and one pistillate flower per inflorescence, glabrous, without appendages on the carpels. However, the new species presents divergent characters, such sessile stamens (vs stamens with filaments), pistillate flower with subglobose (vs ellipsoid) ovary and short-pedicellated fruit, less than 1 cm (long vs long-pedicellated fruit, 2-3 cm long). We provide a diagnosis, morphological description, distribution map, illustrations, and notes on phenology, preliminary conservation status, taxonomic comments and identification key for Atlantic Forest species.