CARLSWARD, BARBARA S.1* and W. MARK WHITTEN2. 1Department of Botany, University of Florida, Gainesville, FL 32611-8526; 2Florida Museum of Natural History, University of Florida, Gainesville, FL 32611-7800. - Molecular systematics of leafless Vandeae (Orchidaceae): An example from tropical America.
Leafless members of tribe Vandeae (Orchidaceae) have undergone extreme
reduction in habit and represent a novel adaptation to the canopy
environment. In these leafless orchids, photosynthetic leaves are
absent or reduced and deciduous. Instead, green roots have assumed the
role of food-assimilation. Many also possess an extremely condensed
stem, making the plant appear "shootless." Vandeae form a
large, pantropical group of orchids traditionally divided into three
subtribes: Aeridinae, Aerangidinae, and Angraecinae. Leafless taxa
occur throughout Vandeae and are geographically distributed in Africa,
Asia, and tropical America. While the most widely accepted
classification system is based solely on floral morphology, our study
was based upon sequence data primarily from ITS nrDNA. Preliminary
results from this nuclear data set indicate the African Aerangidinae
form a paraphyletic grade from which the African and Madagascan
Angraecinae are derived. The Asian Aeridinae, however, do form a
well-supported clade. Phylogenetic relationships of leafless
neotropical Angraecinae (Dendrophylax, Harrisella,
Polyradicion, and Campylocentrum) were estimated using
combined nuclear (ITS) and plastid (trnL-F) data sets, with
African Angraecum species as outgroups. Our molecular analyses
support only two monophyletic genera, Campylocentrum and a
broad Dendrophylax, which seem to indicate that traditional
approaches of classification, based primarily on floral morphology,
are not predictive of phylogenetic relationships.
Key words: Aerangidinae, Aeridinae, Angraecinae, ITS, Orchidaceae, Vandeae