Cladistic studies (morphology + molecules) and developmental studies were used to gain insight into the evolution of androecial characters in the neotropical subtribe Dichorisandrinae, tribe Tradescantieae (Commelinaceae), which consists of Cochliostema (2 spp.), Dichorisandra (25+ spp.), Geogenanthus (5 spp.), Siderasis (2-3 spp.), and a fifth, soon-to-be-described genus (ca. 6 spp.). Within the subtribe, there is a tendency towards reduction from six fertile stamens per flower to five or three. This tendency is particularly strong in the clade (Geogenanthus (Cochliostema, undescribed genus)). The number of fertile stamens in Cochliostema and the undescribed genus is consistently three, although there is considerable variation in expression of the three remaining members of the androecium. Developmental studies in these two genera reveal that three staminodes are usually initiated in the same manner as the fertile stamens but, at anthesis, they vary among species from being relatively large and showy to vestigial. Developmental studies in Geogenanthus, in which the fertile stamens may be either five or six, reveal that in flowers with five stamens, the missing stamen is either not initiated or is early-abortive and vestigial in the mature flower. In addition, although the number of stamens is usually constant for any given species, there is some infraspecific variability in Geogenanthus.

Key words: Cochliostema, Dichorisandra, Geogenanthus, Siderasis, stamen development