Mark studies evolutionary relationships among orchids of the group Pleurothallidinae, particularly the genus Pleurothallis. These orchids occur as epiphytes in high-elevation cloud forests from southern Mexico, through Central America, into the Andean countries of Venezuela, Colombia, Ecuador, Peru, and Bolivia. Through field work and collaborations with individuals and botanic gardens in each of these locations, Mark is collecting living plants or samples of the described species in the genus Pleurothallis in order to generate a molecular phylogeny representing possible evolutionary relationships in the genus. Molecular phylogenies such as this are developed through comparison of sequences in the nuclear or chloroplast genomes. This phylogeny will provide the basis for determining whether segregate, monophyletic genera can be created from species within the huge, highly diverse genus Pleurothallis. The research will also lead to the development of a database of DNA sequences unique to each Pleurothallis species, a so-called “DNA barcode,” such that in the future, identifications can be made even by untrained taxonomists, from a small sample of any plant in the genus, just by sequencing the appropriate DNA regions and comparison to the database. In addition to rapid identification, the barcoding can indicate that a species is not in the database and probably is undescribed, a “new” species. Mark has already collected several undescribed species, which will be described and named in the future.