Bicarpellate gynoecium in two species of Senna (Fabaceae, Caesalpinioidae, Cassiinae)

ABSTRACT Flowers of species of Senna are very morphologically diverse, however, nothing has been reported regarding variation in the presence of a unicarpellate gynoecium, which is characteristic of the group. This study reports the occurrence of a bicarpellate gynoecium in two enantiostylous species of Senna in an area of dry forest (Caatinga) in NE Brazil. Observations of floral morphology and estimates of the proportions of floral morphs in the populations were performed. The species produce three floral types: left (L), right (R) and bicarpellate (B). The proportion of these floral morphs were similar in the populations of Senna macranthera var. micans, but the number of B flowers in populations of S. trachypus was lower than that recorded for L and R flowers. The occurrence of this morphological variation may be related to enhancing pollen capture in both species; in S. trachypus, this variation may also be related to reducing florivory by caterpillars that were observed eating sexual elements of the flowers.