Graduate Thesis Or Dissertation
 

Biosystematics of parsley-ferns, Cryptogramma R. Br., in western North America

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  • A biosystematic investigation of Cryptogramma section Cryptogramma in western North America has been directed towards resolution of two separate taxonomic questions. Results of this research support the hypothesis that a previously undescribed diploid (2n = 30 II) taxon, C. cascadensis, is present along with the common and widespread C. acrostichoides. The new species is distinguished by a number of subtle but constant morphological features, including sterile fronds that are soft and deciduous (compared to the coriaceous, evergreen sterile leaves of C. acrostichoides); surficial rather than sunken hydathodes; absence of laminar trichomes, and significantly smaller spores. Data from enzyme electrophoresis confirm the separation of C cascadensis as a distinct species, as 6 of 13 loci scored were "marker loci", with no alleles held in common between the two species. While different populations of the same species were genetically similar, with genetic identities > 0.85, the mean genetic identity for interspecific population comparisons was 0.36, demonstrating a substantial amount of genetic divergence between the two species. Both species were found to be primarily outcrossing, and the existence of marker loci and a high degree of allozymic differentiation, even in mixed populations, suggests that the two species are reproductively isolated. Also investigated was the taxonomy and evolutionary origin of Cryptogamma sitchensis, a taxon previously treated as a variety of C. acrostichoides. Cryptogamma sitchensis was found to be a tetraploid species, with 2n = 60 II, the first report of polyploidy in the genus from North America. Data from enzyme electrophoresis showed fixed heterozygosity, a characteristic of allopolyploid species. Allozyme banding patterns showed that C. sitchensis combines genomes of C. acrostichoides and another distinct species not present in North America. Morphological characters, particularly the dissection of sterile leaves, suggested that this second parent is the eastern Asian C. raddeana. Frequent triploid hybrids, which can be identified by their abortive spores, occur where the ranges of C. sitchensis and C acrostichoides overlap. Hybrids blur the morphological distinctions between the two species, and are probably responsible for leading earlier workers to conclude that the taxa are only varietally distinct. These results have implications for systematic treatment of other taxa in section Cryptogramma, suggesting that the best taxonomic approach may be to treat geographic segregates as distinct species, rather than as varieties or subspecies of a single circumboreal species, C. crispa, as has been proposed by some workers.
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