A PHYLOGENETIC ANALYSIS OF SUBTRIBE PLEUROTHALLIDINAE (ORCHIDACEAE)

A cladistic analysis of subtribe, Pleurothallidinae (Orchidaceae) is b ased on 45 anatomical/morphological characters. The ingroup members co mprise 24 genera; the large genus Pleurothallis consists of two subgen era and ten species complexes. Three taxa representing subtribes Laeli inae and Arpophyllinae are designated as outgroup. Eight most parsimon ious trees were discovered using computer assisted software (length = 230; CI = 0.27). The hypothesis that subtribe Pleurothallidinae has un dergone a unilinear reduction in the number of pollinia is not support ed by this study. Although the eight-pollinia slate as represented by Octomeria apparently is plesiomorphic, the two-pollinia and four-polli nia states arose early in the phylogeny of the subtribe. Both two and four-pollinia states subsequently reappeared as parallelisms. The six- pollinia state exhibited in Brachionidium is autapomorphic. This cladi stic analysis suggests that Pleurothallis is not a natural genus and, perhaps may be divided into several discrete genera.