HARDY, CHRISTOPHER R.1,2*, ROBERT B. FADEN3, JERROLD I. DAVIS1 AND DENNIS WM. STEVENSON2,1. 1L.H. Bailey Hortorium, Cornell University, Ithaca, NY 14853-4301, 2New York Botanical Garden, Bronx, NY 10458-5126, and 3Department of Botany, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560-0166. - A phylogenetic and developmental approach to understanding androecium evolution in the subtribe Dichorisandrinae (Commelinaceae).
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