Biosystematic Analysis of the Cystopteris tennesseensis (Dryopteridaceae) Complex

Abstract

The allotetraploid Cystopteris tennesseensis and its putative diploid progenitors, C. bulbifera and C. protrusa, constitute the C. tennesseensis complex. Although previous studies provided evidence of morphological, ecological, and chromosomal differences among the members of this complex, puzzling morphological variability precluded consistent identification and treatment of the taxa. The current study combined morphometric analyses with surveys of chromosomal, isozymic, and gametophytic features and supported past treatments of the complex as three separate species. The diploids shared no allozymes for the nine enzymes examined, and meiotic analyses of triploid hybrids with C. tennesseensis provided additional evidence that the diploid genomes are nonhomologous. Because C. tennesseensis has a relatively narrow range and contains isozymic profiles that are consistently additive of diploid patterns, we suggest that this allopolyploid is a relatively young species. Isozymic variation in the tetraploid parallels that observed in the diploids, implying that genetic variability was introduced through recurrent hybridization. Analyses of isozymic data and gametophytic features indicated that the diploids outcross frequently and thus may form hybrids readily when sympatric with the tetraploid. In part because of these characteristics, precise identification of species and hybrids in this complex is difficult and depends on evaluation of cryptic features.