A Reevaluation of Lycopodium porophilum and Its Relationship to L. lucidulum (Lycopodiaceae)

Multivariate analyses of morphological data from both pure and mixed natural pop- ulations of Lycopodium lucidulum and L. porophilum support the recognition of L. porophilum as a species distinct from L. lucidulum. Hybridization between these species accounts for the sterile intermediates observed in mixed populations. Patterns of co-occurrence and experimental data demonstrate a genetic rather than an environmental basis for the observed differences between the species. Lycopodium porophilum Lloyd and Underw., a clubmoss endemic to sandstone cliffs in the east- central United States, was originally described as intermediate between the common temper- ate species L. lucidulum Michaux and the wide- spread boreal and arctic species L. selago L. (Lloyd and Underwood 1900). Although L. po- rophilum has subsequently been recognized as a distinct species (Hill 1911; Fernald 1950; Wherry 1961), this interpretation has not been universal. Wilson (1932) rejected L. porophilum and treated specimens intermediate between L. selago and L. lucidulum as L. selago var. patens (Beauv.) Desv. In doing so, he combined in this taxon plants from sandstone cliff habitats in the central United States with those from alder swamps, bog margins, and wet granitic cliffs in the eastern boreal forest. Preliminary conclu- sions based on herbarium specimens (Water- way 1977) indicate that Wilson's interpretation is incorrect; L. porophilum is distinct from the boreal L. selago var. patens in morphology, hab-