The varieties of Thelypteris pilosa have been recognized as the sole New World members of the subgenus Stegnogramma. Ferns of this species complex are common throughout central and southern Mexico, Guatemala, and Honduras and exhibit an intriguing temperate disjunction in Alabama. A significant amount of morphological variation exists in the Mexican taxa; it is unclear whether these differences are due to phenotypic plasticity or genetic factors. Two regionally sympatric morphotypes, varying from deltate to lanceolate fronds, occur throughout Mexico and have been described as var. major and var. pilosa, respectively. A more distinct type, described as var. alabamensis, is endemic to north Alabama rockhouse habitats and has been reported from only a single county. Data on ecology, spore morphology, gametophyte biology, and gross frond morphology support the elevation of T. pilosa var. alabamensis to specific status under the proposed name of T. burksiorum.