Morphometric circumscription of species and infraspecific taxa in Calopogon R.Br. (Orchidaceae)

Abstract.

The orchid genus Calopogon contains five species, the widespread C. tuberosus containing three varieties. The members of this small genus have a history of circumscriptional uncertainty, suggesting the need for further taxonomic evaluation. To determine characters distinguishing different groups and to examine their circumscription, we performed morphometric analyses on two different subsets of Calopogon, one of all the currently recognized species of the genus and another of only C. tuberosus, based on 40 vegetative and floral variables measured from live plants. Principal components analyses (PCA) generally did not detect highly distinct groups, but canonical variate analyses (CVA) identified numerous characters that readily distinguish most of these groups, the least distinguishable of these being C. tuberosus var. latifolius. Furthermore, generalized patterns of similarity between taxonomic and geographic subdivisions within C. tuberosus were further examined on a plant-by-plant basis using squared Mahalanobis distances determined from the CVA of this species. Finally, using three different tests, the degree of morphological diversity was examined for each of the different groups of C. tuberosus, finding that the northern range of the species contained less diversity whereas the southern range generally contained more. We maintain the recognition of all Calopogon taxa except C. tuberosus var. latifolius, and do not recognize any new taxa based on our examinations of geographic partitions of the typical variety of C. tuberosus. However, morphology was observed to vary substantially over the geographic range of the typical variety and this species overall.