Unraveling the origin of the Appalachian gametophyte, Vittaria appalachiana.

Premise Of Study: Ferns and lycophytes are distinct among plants in producing two free-living life stages: a long-lived sporophyte phase and a (usually) short-lived gametophyte phase. Notably, however, some species have perennial, vegetatively reproducing gametophytes. Vittaria appalachiana is one of just three species in which mature sporophytes are unknown. It has a wide range throughout the Appalachian Mountains and Plateau, where it reproduces asexually via gemmae. The origin of V. appalachiana, however, has long been a mystery, with most previous studies suggesting it may have resulted from hybridization of two closely related Vittaria species (V. graminifolia and V. lineata).

Methods: A four-gene plastid data set including 32 samples of six Vittaria species, plus samples of five outgroup species, was analyzed to uncover phylogenetic relationships. Additional analyses of nuclear DET1 gene sequences allowed for the examination of hypotheses involving a hybrid origin for V. appalachiana.

Key Results: In the plastid phylogeny, V. appalachiana is well supported as monophyletic, but is embedded within V. graminifolia. With the exception of a single aberrant allele, this result is mirrored in the nuclear tree.

Conclusions: Through analyses of plastid and nuclear data sets, this study demonstrates that a hybrid origin for V. appalachiana is unlikely. Instead, it appears that this species emerged from within the V. graminifolia lineage. Further work is needed to fully elucidate the genetic structure within this group.