The orchid genus Pleurothallis is believed to be predominantly fly-pollinated based on limited field studies. I hypothesized that both reward and deceit pollination syndromes occur in the genus and deceit pollination, more specifically, pseudocopulation has evolved more than once. Flowers were sampled from several infrageneric groups within Pleurothallis and examined by scanning electron microscopy. Morphological features of the labellum of the flower, such as the presence or absence of a glenion or other secretory tissue, or cavities possibly involved in pseudocopulation, were used to infer possible pollination mechanisms. Additionally, new nuclear ITS and plastid 3’ ycf1 sequences were added onto the phylogenies generated by previous students in Wilson Laboratory. Pollination mechanisms inferred from floral morphology was mapped onto the phylogenies. Preliminary data suggest that pseudocopulation may have evolved more than once in Pleurothallis.
Pleurothallis is the largest myophilous (fly-pollinated) genus in subtribe Pleurothallidinae. Although many studies show highly specific relationships in pollination systems in the Orchidaceae, our understanding of these relationships in myophilous orchids is almost non-existent (Borba & Semir 2001). This study focuses on the floral micromorphology, specifically the lip and column, of species within subgenera Ancipitia and Scopula. Scanning electron microscopy of the micromorphology of floral structure shows a range of morphology and pollination mechanisms within the two studied subgenera. These include deceit pollination by pseudocopulation and reward pollination. In concert, phylogenetic analysis was performed to determine if a correlation existed between morphology or pollination mechanism and taxonomic groupings. Maximum parsimony trees were produced using ITS and matK sequences for subgenera Ancipitia, Scopula, and Pleurothallis, with species from the genera Laelia, Pabstiella, and Arpophyllum as outgroups. The ITS, matK and combined trees strongly support an Ancipitia/Scopula section within a monophyletic subgenus Pleurothallis. Within this section, both reward and deceit pollination mechanisms are found, meaning they are not restricted to the current taxonomic groupings. Morphological and genetic data therefore support the grouping of subgenera Ancipitia, Scopula, and Pleurothallis into one monophyletic subgenus.
The appropriate taxonomic organization of Pleurothallis (subtribe Pleurothallidinae, family Orchidaceae) and its subgenera has been debated for more than a century. Recent phylogenetic studies have suggested that subgenera previously elevated to the level of genus based on morphological studies are most appropriately considered subgenera of Pleurothallis. This study analyzed the hypothetical open reading frame ycf1, a plastid gene, in order first to determine its utility in phylogenetic study at the generic and infrageneric level, and second to test support for the existing models or suggest a new model for taxonomic organization of Pleurothallis. A 1,200 bp 5’ region and a 1,500 bp 3’ region of the ycf1 gene were sequenced for representative species of each of the morphologically-based groups within Pleurothallis sensu lato and phylogenetic trees were generated for each region using maximum-parsimony analysis. The tree generated from the 5’ region exhibited minimal topological structure, suggesting either that the species sequenced are too closely related to be segregated into unique genera or the 5’ region of the gene did not contain enough parsimony informative sites to be useful at this level of study. The 3’ ycf1 gene tree had considerably more topology but the small number of species sequenced limits the conclusions that can be drawn from the phylogenetic tree.