WATKINS, JR., JAMES E.* AND DONALD R. FARRAR. Iowa State University, Department of Botany, 353 Bessey Hall, Ames, IA 50011. - Biosystematic investigation of the rare, disjunct, rockhouse fern Thelypteris pilosa var. alabamensis (Thelypteridaceae: Stegnogramma).
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