No abstract

Molecular data from the chloroplast genome are being used to reconstruct the phylogeny and revise the problematic taxonomy of the xerically adapted cheilanthoid ferns. Chloroplast DNA based phylogenies trace maternal, paternal, or biparental lineages, depending on the mode of inheritance of the chloroplast genome, and instances of all three modes of inheritance are known in the seed plants. Evidence for biparental and uniparental inheritance in ferns has been presented, but the distinction between maternal and paternal uniparental inheritance has not been rigorously made, and the mode of inheritance in cheilanthoid ferns is completely unknown. Based on a natural hybrid population in the cheilanthoid genus Pellaea in which the maternal and paternal derivations of the hybrid are unambiguously known, restriction fragment length polymorphisms of chloroplast DNA demonstrated simple maternal inheritance of the chloroplast genome. This hybrid complex was also examined for restriction fragment length polymorphisms of its mitochondrial DNA, providing the first direct evidence that the mitochondrial genome in ferns is maternally inherited.

Convergent evolution driven by adaptation to arid habitats has made It difficult to identify monophyletic taxa in the cheilanthoid ferns. Dependence on distinctive, but potentially bomoplastic characters, to define majcr clades has resulted in a taxonomic conundrum: all of the largest cheilanthoid genera have been shown to be polyphyletic. Here we reconstruct the first comprehensive phylogeny of the strictly New World cheilanthoid genus Argyrochosma. We use our reconstruction to examine the evolution of farina (powdery leaf deposits), which has played a prominent role in tbe circum.scription of cheilanthoid genera. Our data indicate that Argyrochosma comprises two major monophyletic groups: one exclusively non-farinose and the other primarily farinose. Within the latter gioup, there has been at least one evolutionary reversal (loss) of farina and the development of major chemical variants tbat characterize specific clades. Our phylogenetic hypothesis, in combination with spore data and chromosome counts, also provides a critical context for addressing the prevalence of polyploidy and apomixis within the genus. Evidence from these datasets provides testable hypotheses regarding reticulate tvolution and suggests the presence of several previously undetected taxa oí Argyrochosma.

Although analyses of chromosome numbers represent a fundamental step in the study of any group of organisms, the xeric-adapted cheilanthoid ferns (Pteridaceae: subfamily Cheilanthoideae) have received little attention from cytogeneticists due to the difficulty in obtaining samples and accurate chromosome counts. In an effort to clarify patterns of chromosomal evolution in this group, we present 131 chromosome counts representing 75 taxa of cheilanthoid ferns from the western United States and Mexico. First reports are provided for 24 taxa, including the first count for the genus Cheiloplecton. Nine other taxa yielded numbers that had not been reported previously. Our data suggest that chromosome base numbers are more stable than previously thought and that much of the reported variation may involve erroneous counts. When coupled with published DNA sequence data, our counts suggest that the plesiomorphic base number of subfamily Cheilanthoideae is x = 30 and that x = 29 has arisen just once or twice among the taxa studied.

The brake fern genus Pteris belongs to the Pteridaceae subfamily Pteridoideae. It contains 200-250 species distributed on all continents except Antarctica, with its highest species diversity in tropical and subtropical regions. The monophyly of Pteris has long been in question because of its great morphological diversity and because of the controversial relationships of the Australian endemic monospecific genus Platyzoma. The circumscription of the Pteridoideae has likewise been uncertain. Previous studies typically had sparse sampling of Pteris species and related genera and used limited DNA sequence data. In the present study, DNA sequences of six plastid loci of 146 accessions representing 119 species of Pteris (including the type of the genus) and 18 related genera were used to infer a phylogeny using maximum-likelihood, Bayesian-inference and maximum-parsimony methods. Our major results include: (i) the previous uncertain relationships of Platyzoma were due to long-branch attraction; (ii) Afropteris, Neurocallis, Ochropteris and Platyzoma are all embedded within a well-supported Pteris sensu lato; (iii) the traditionally circumscribed Jamesonia is paraphyletic in relation to a monophyletic Eriosorus; (iv) Pteridoideae contains 15 genera: Actiniopteris, Anogramma, Austrogramme, Cerosora, Cosentinia, Eriosorus, Jamesonia, Nephopteris (no molecular data), Onychium, Pityrogramma, Pteris, Pterozonium, Syngramma, Taenitis and Tryonia; and (v) 15 well-supported clades within Pteris are identified, which differ from one another on molecular, morphological and geographical grounds, and represent 15 major evolutionary lineages.

No abstract

Molecular data from the chloroplast genome are being used to reconstruct the phylogeny and revise the problematic taxonomy of the xerically adapted cheilanthoid ferns. Chloroplast DNA based phylogenies trace maternal, paternal, or biparental lineages, depending on the mode of inheritance of the chloroplast genome, and instances of all three modes of inheritance are known in the seed plants. Evidence for biparental and uniparental inheritance in ferns has been presented, but the distinction between maternal and paternal uniparental inheritance has not been rigorously made, and the mode of inheritance in cheilanthoid ferns is completely unknown. Based on a natural hybrid population in the cheilanthoid genus Pellaea in which the maternal and paternal derivations of the hybrid are unambiguously known, restriction fragment length polymorphisms of chloroplast DNA demonstrated simple maternal inheritance of the chloroplast genome. This hybrid complex was also examined for restriction fragment length polymorphisms of its mitochondrial DNA, providing the first direct evidence that the mitochondrial genome in ferns is maternally inherited.

Restriction site variation in chloroplast DNA was examined in the neotropical fern genus Phanerophiebia and in selected species of the related Asiatic genus Cyrtomium and the cosmopolitan progenitor of these two, Polystichum. The chloroplast genome has been shown to possess great potential as a tool for the assessment of evolutionary relationships among plants. Physical and gene mapping and/or comparative analysis of restriction endonuclease site mutations have been used by many workers to study problems at both specific and generic levels in various plant groups (1-10). The latter approach is particularly well suited for studies of evolutionary divergence within species complexes, and the highly conserved nature of chloroplast DNA and relatively low levels of homoplasy facilitate the construction of relatively unambiguous phylogenies using cladistic analysis.