The homosporous pteridophytes have been largely uninvestigated by electrophoresis, despite the fact that they offer many exciting research possibilities (Soltis et al., 1980). The paucity of electrophoretic studies of ferns and fern allies may be due in large part to the high concentrations of condensed tannins that many species contain (Cooper-Driver, 1976 and pers. comm.). These compounds render enzymes inactive by binding with them following cellular disruption, thereby frustrating researchers who have attempted electrophoretic analysis utilizing standard methods of sample preparation.The method of sample preparation developed by Kelley and Adams (1977a, b) in their analysis of enzyme variation in Jimiperus was an important procedural breakthrough in overcoming the difficulties that result from the liberation of large amounts of phenolic compounds during tissue preparation. Recently, a simplified version of that method was applied by Soltis et al. (1980) to fern leaf tissue, facilitating rapid preparation of active enzyme samples and thereby making electrophoretic analyses of large numbers of individuals more feasible.In an attempt to improve methods of analysis of fern enzymes in starch gel electrophoresis, we have experimented with modifications of the method of sample We M Werth fern tissue. Finally, during the course of our electrophoretic investigations of ferns we found that standard gel and electrode buffers and staining schedules, such as those of Brewer (1970) and Shaw and Prasad (1970), often provided unsatisfactory results when applied to ferns. We have determined gel and electrode buffers, as well as staining schedules, that provide clear starch gel enzyme banding for 22 enzyme systems in ferns. Requests for advice resulting from the recent surge of interest in fern enzyme electrophoresis have prompted us to compile our procedural data so that other researchers can take advantage of our experimentation. We hope that these data will stimulate more extensive electrophoretic investigation of pteridophytes and other electrophoretically difficult taxa. Gottlieb (1981b) recently reviewed aspects of enzyme electrophoresis primarily in gymnosperms and angiosperms. His discussion is equally relevant to understanding the potential applications and limitations of electrophoretic evidence in pteridophytes. Since homosporous pteridophytes have high chromosome numbers, it is tempting to invoke polyploidy in interpreting their enzyme band patterns. It is well
Nucleotide sequences of the chloroplast DNA gene rbcL were determined for 2b species of cheilanthoid ferns (Pteridaceae subfamily Cheilanthoideae]. Together with GenBank sequences of an additional cheilanthoid and a 14-species outgroup comprising Pteridaceae, Vittariaceae, and Coniogramnie japonica, these were analyzed cladistically by maximum parsimony to gain insights into cheilanthoid phylogeny and generic circumscriptions, which have long stymied pteridologists. Our analysis yielded 4 equally most parsimonious trees of 1570 steps. Two of these trees varied only in the relative positions of Onychium and Pteris in the global outgroup, The other two varied only in the relative positions oi Pellaea pringlei and P. rotundifolia in the ingroup. Results based on rbcL sequences are concordant with those of recent studies of Argyrochosma, Hemionitis, and Bommeria that utilized a broad suite of characters, suggesting that rbcL-based inferences in less meticulously studied cheilanthoid groups also convey meaningful information. Among the insights into cheilanthoid phylogeny and generic circumscriptions offered by rbcL sequences are the following. Llavea does not belong in subfamily Cheilanthoideae. Pellaea and Cheilanthes are polyphyletic. The recent removal of 21 species from Notholaena to Cheilanthes and the segregation of Argyrochosma are supported. The transfer of Hemionitis elegans to Bommeria is strongly supported, but the removal of the group of Doryopteris concolor to Cheilanthes is not. Trachypteris is sister to Doryopteris. The segregation of some small genera from Cheilanthes is supported, but these require further study through inclusion of additional taxa. Bommeria is the most basal ingroup element in this analysis.
Cheilantho ids are the most commonl y e ncountered fe rn species of the arid southwest and other xeric habitats throughout the world. Cheilanthes, Notholaena, Pellaea, and Bommeria are the best known southwestern genera, but some authors recogni ze segregate genera such as Argyrochosma, Aspidotis, Astrolepis, and Pentag ramma. Others reject di stinctions among some of these genera as artificial, leaving cheil antho id generic concepts in a state of flu x. This unsettl ed taxonomy is often attributed to morpholog ical homoplasy associated with adaptation to xeric habitats , suggesting the need for new analyses that do not depend o n potentially mi sleading morphology. Nucleotide sequences of the maternally inherited, chloroplast-encoded rbcL gene from 57 species that bear on the relationships of the cheilanthoids of the southwest were c1adistically analyzed under the optimality criterion of max imum parsimony. The results provide new insights into phylogeneti c re lationships and ge neric circumscriptio ns of these ferns. Mexican Llavea cordifolia is rejected from the cheilantho ids, traditio nal Cheilanthes, Notholaena, and Pellaea are polyphyletic, and the segregati ons of A rgyrochosma, Aspidotis, Astrolepis, and Pentag ramma are supported. To assess confidence in these conclusions, results of the rbcL-based analys is are compared with those based on ITS sequences of biparentall y inherited nucl ear ribosomal DNA (nrDNA) for a subset of cheil anthoid taxa. These two data sets yield remarkabl y congruent topologies at shall owe r phylogenetic levels, suggesting that previous taxonomic proble ms in thi s g roup may indeed be attributable to diffi culties in inte rpreting the taxonomic significance of morphological characters . Disagreement at deeper levels of the topologies suggests the need to incorporate data from less rapidly evolving nrDNA regions.
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.
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