Morphological Studies of Chamaecrista sect. Absus ser. Setosae (Leguminosae) With Emphasis on the Chamaecrista setosa Complex, Including a New Species

Chamaecrista is one of the largest genera of Leguminosae, subfamily Caesalpinioideae. Traditionally, it has been divided into six sections, of which Chamaecrista sect. Absus is the largest, with 31 series. Chamaecrista sect. Absus ser. Setosae comprises nine species. Chamaecrista setosa is the most widely distributed species, comprising four varieties, distinguished by the type and distribution of glandular trichomes, and the leaflet venation. Given the importance of leaflet venation in the delimitation of the taxa, here we performed a study of leaflet architecture of all species of the series and a more detailed morphological study for the Chamaecrista setosa complex. For the study of leaf architecture, 2D images of the leaflets were made using the Faxitron x-ray technique. The morphological studies were based on herbarium specimens. We present the details of the leaflet architecture for the species of Chamaecrista sect. Absus ser. Setosae, and we propose nomenclatural changes for a variety of Chamaecrista setosa and some corrections to typifications. During our studies we also found a new species, Chamaecrista forzzae, which is morphologically similar to Chamaecrista setosa and Chamaecrista multiseta. It is here described and illustrated.