Chloroplast Dna Restriction Site Variation in the Fern Genus Pellaea: Phylogenetic Relationships of the Pellaea Glabella Complex

Abstract

The cheilanthoid ferns have long resisted efforts to circumscribe well‐defined, phylogenetically natural generic and infrageneric groups, presumably because of homoplastic morphologies associated with their xeric habitats. This cladistic analysis of phylogenetically informative chloroplast DNA restriction site data from 14 enzymes and seven taxa in the cheilanthoid genus Pellaea provides new insights into the phylogenetic relationships of the P. glabella complex. It also assesses the congruence of results based on restriction site data at inter‐ and intraspecific levels in these sexually and apogamously reproducing ferns with those of earlier morphological and isozyme analyses of the same group. Wagner parsimony yielded a single most parsimonious tree of 187 steps and 11% homoplasy, based on a data matrix of 166 restriction sites of which 66 were phylogenetically informative. Phylogenetic analysis based on user‐defined stepmatrix character‐state weighting of site gains over losses produced an identical single most parsimonious tree. Dollo parsimony yielded two most parsimonious trees, one of which was topologically identical to the Wagner tree. Specific and infraspecific relationships in the P. glabella complex determined by the completely independent restriction site and isozyme data sets are identical. This lends confidence to the ongoing use of restriction site data in a broader study of Pellaea and other cheilanthoid taxa and to the present conclusions that P. atropurpurea is sister to the P. glabella complex, whereas P. breweri, previously considered the closest relative of this complex, is actually more distantly related to it than are the other taxa in this study.

Phylogeny of the Polypodium vulgare Complex: Insights from Chloroplast DNA Restriction Site Data

“…Studies of other fern congeners are revealing similarly high sequence divergence values (e. g., Gastony et al 1992). Based on these observations, it may be possible to obtain highly resolved phylogenetic hypotheses within fern genera using cpDNA restriction site data.…”

“…Because the average genetic identities (Nei 1972) among members of the P. vulgare complex were quite low (I = 0.34, Haufler et al 1995), it seemed reasonable to apply the more slowly evolving cpDNA molecule in comparing relative divergences within and between subgeneric groups. In addition, because chloroplasts appear to be maternally inherited in ferns (Gastony and Yatskievych 1992), we hoped to identify the maternal progenitors of the tetraploid species. In this paper, we used cpDNA restriction site variation in members of the P. vulgare complex as well as from tropical outgroup species to: 1) resolve phylogenetic relationships among diploid members of the P. vulgare complex, and 2) gain new insights into the origins of the tetraploids.…”

“…and related genera and developed new insights for understanding historical relationships among these ferns. At the generic level, Gastony et al (1992) used restriction site data to test hypothesized species groupings in Pellaea Link. These successes suggested that cpDNA features could be applied in reconstructing aspects of the evolutionary history of the Polypodium vulgare L. species complex.…”