Thelypteris pilosa, has been recognized as the sole member of the subgenus, Stegnogramma, in the new world. This taxon is common throughout central and southern Mexico, Guatemala and Honduras, and exhibits an intriguing temperate disjunction in Alabama. Past taxonomic studies have suggested that the Old World T. pozoi is closely allied to T. pilosa adding these taxa to the list of Asian American disjuncts. A significant amount of morphological variation exists in the Mexican taxa and it is unclear whether these differences are due to phenotypic plasticity or genetics. Two regionally sympatric morphotypes, terrestrial with deltate fronds and epipetric with lanceolate fronds occur throughout Mexico. These two types 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, gametophyte biology, crossing studies, spore morphology, and molecular biology question the varietal distinction of the Mexican material but support the elevation of T. pilosa var. alabamensis to specific status under the proposed name of T. burksiorum. Insights into the origin and taxonomic affinities of the Old and New World species are presented.

Key words: Stegnogramma, disjunction, pteridophyte, Thelypteris pilosa