Registered users receive a variety of benefits including the ability to customize email alerts, create favorite journals list, and save searches.
Please note that a BioOne web account does not automatically grant access to full-text content. An institutional or society member subscription is required to view non-Open Access content.
Contact email@example.com with any questions.
Athyrium filix-femina (Lady Fern) comprises a complex of homoploid (n = 40) taxa, distributed over much of the northern hemisphere and extending into South America, whose evolutionary relationships are poorly understood and whose taxonomic treatment is problematic. The A. filix-femina complex of North America comprises as many as four taxa with overlapping ranges and provides an especially suitable context for exploring patterns and processes of divergent evolution and its taxonomic consequences in ferns. We addressed differentiation of two eastern North American taxa distinguished on the basis of growth form, frond shape, and spore color, and most recently treated as varieties A. angustum and A. asplenioides (Northern and Southern Lady Fern respectively). Although, these two taxa have been long perceived as closely related, they have been known to intergrade and recombine to form a hybrid zone in their relatively narrow region of overlap. This perception is supported by the data from the present study. Collections from 17 populations, 9 of A. angustum from Quebec to Pennsylvania and 8 of A. asplenioides from New Jersey to North Carolina, were examined for spores using LM, SEM, and TEM, and/or allozymes (16 loci coding 10 enzymes). The two taxa exhibited highly distinct perispore surfaces: all A. angustum individuals had papillose surfaces, whereas most A. asplenioides individuals were rugose with a reticulum of inflated folds. Spores from the northernmost A. asplenioides population sampled (Shirley, NJ) showed varying degrees of intermediacy suggestive of introgressive hybridization with A. angustum. Levels of allozyme polymorphism in populations (means: P=36.5%, A=1.97, HE=0.129) were near means for angiosperms and ferns. Genotype frequencies at most loci in all populations were in Hardy-Weinberg equilibrium indicating an outcrossing mating system. Most alleles were shared among all populations. However, at the four most polymorphic loci (Idh-1, Pgi-2, Pgm-2, and Tpi-2) allele frequencies were significantly divergent between populations of A. angustum and A. asplenioides, especially Idh-1 which approached fixation for alternate alleles. Values for FST ranged from 0.008 to 0.459 for individual loci (0.255 across loci) with especially high values for Idh-1, Pgi-2, Pgm-2, and Tpi-2. Hierarchical FST analysis indicated that differences between the two taxa (FXY=0.216) accounted for most allele frequency divergence among populations (FXY=0.238). UPGMA analysis of paired Rogers' Similarity (S) values resulted in two principal clusters each comprising populations of one taxon. Populations of A. angustum and A. asplenioides were joined within their clusters at S=0.938 and S=0.945 respectively, while the two taxon clusters were joined at S=0.848. The spore and isozyme data indicate substantial divergence between A. angustum and A. asplenioides, suggesting that they merit distinction at the rank of subspecies or species. Additional study of populations in their region of sympatry is required to determine the nature and extent of hybridization.
With its thick, leathery leaves, reticulate venation, and large sori, Polypodium scouleri, located in a narrow band along the Pacific coast of North America, is the most distinctive member of the cosmopolitan P. vulgare species complex. Although early studies based on morphology and chromosomes yielded hypotheses about the relationships among some elements of this complex, phylogenetic alliances to P. scouleri were not proposed. Combining data from rbcL and trnL DNA sequences with isozymic analyses suggested that P. scouleri originated relatively recently and is closely allied to and sympatric with P. californicum and P. glycyrrhiza. Consistent with a hypothesis of recent origin, we detected no infraspecific isozymic variation across the range of P. scouleri. Although allopolyploidy is a common feature of the P. vulgare complex, P. scouleri stands out because it has not been implicated in the origin of any secondary (allotetraploid) species. However, as early as 1951, Manton reported a triploid individual that was morphologically similar to P. scouleri, but whose other parent could not be verified. Since that time, others have suggested that P. scouleri might be crossing with sympatric congeners, but no solid evidence has been obtained. The present study confirmed that P. scouleri hybridized with neighboring P. calirhiza, and showed that individuals with intermediate morphological features contained isozyme marker alleles from both parental lineages.
The prothallial development of gametophytes of Olfersia alata and Olfersia cervina (Dryopteridaceae) is described and compared. Spores are monolete, ellipsoid, and with broadly winged perispore. Germination is Vittaria-type and the prothallial development is Aspidium-type. Adult gametophytes are cordiform-spatulate to cordiform-reniform, with marginal and superficial trichomes. Gametangia are of the type commonly found on leptosporangiate homosporous ferns. Differences between the two species of genus include size of the spores, width of the perispore, germination time, size of the trichomes, and time of formation of the gametangia. These two species share some features with some species of Arachniodes, Cyrtomium, Dryopteris, Phanerophlebia, and Polystichum, such as type of germination and prothallial development and trichomes. They differ from Didymochlaena truncatula, which has prothallial development of the Adiantum-type and lacks trichomes on the sexual phase.