The genus Calopogon consists of five species and three varieties of terrestrial orchids. Three species, C. barbatus, C. multiflorus, and C. pallidus are found in coastal plain savannas of the south-eastern United States. Another species, C. oklahomensis, recently described, is found in prairies and savannas from Minnesota south to Texas and Louisiana. The fifth species, C. tuberosus, consists of three varieties, var. tuberosus, found in bogs and savannas from Texas and Manitoba, east to the Atlantic coast, var. latifolius, found in maritime bogs in eastern Canada, and var. Simpsonii, found in alkaline savannas in the Bahamas, Cuba, and south Florida. ITS sequences were obtained for 57 populations within the genus, representing the geographic and morphological extremes of each taxon. AFLP data was obtained for 58 plants representing 25 populations within the genus, one artificial hybrid, and one putative natural hybrid. The 25 populations sampled represent the geographic extremes of all taxa. In general, there is considerable agreement between the ITS parsimony analysis and the AFLP UPGMA analysis at the species level, which is congruent with many significant morphological features. AFLP, however, shows greater resolution at the population level, although both data sets generally place sampled populations into previously defined species. ITS data do not refute the distinctiveness of the different varieties of C. tuberosus, due to lack of resolution, whereas AFLP data generally support the varieties. Of particular interest is the intermediacy that both data sets suggest of C. oklahomensis. This species is polyploid, while the other four species are diploid, and numerous morphological features in this species suggests that it may be of hybrid origin. If available, comparisons with plastid RFLP data will also be presented.

Key words: AFLP, Calopogon, circumscription, hybrid speciation, ITS, phylogeny