Cheilanthoid Ferns (Pteridaceae: Cheilanthoideae) in the Southwestern United States and Adjacent Mexico-A Molecular Phylogenetic Reassessment of Generic Lines

Cheilanthoids are the most commonly encountered fern 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 recognize segregate genera such as Argyrochosma, Aspidotis, Astrolepis, and Pentagramma. Others reject distinctions among some of these genera as artificial, leaving cheilanthoid generic concepts in a state of flux. This unsettled taxonomy is often attributed to morphological homoplasy associated with adaptation to xeric habitats, suggesting the need for new analyses that do not depend on potentially misleading 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 cladistically analyzed under the optimality criterion of maximum parsimony. The results provide new insights into phylogenetic relationships and generic circumscriptions of these ferns. Mexican Llavea cordifolia is rejected from the cheilanthoids, traditional Cheilanthes, Notholaena, and Pellaea are polyphyletic, and the segregations of Argyrochosma, Aspidotis, Astrolepis, and Pentagramma are supported. To assess confidence in these conclusions, results of the rbcL-based analysis are compared with those based on ITS sequences of biparentally inherited nuclear ribosomal DNA (nrDNA) for a subset of cheilanthoid taxa. These two data sets yield remarkably congruent topologies at shallower phylogenetic levels, suggesting that previous taxonomic problems in this group may indeed be attributable to difficulties in interpreting 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

The evolution of the plastid chromosome in land plants: gene content, gene order, gene function

This review bridges functional and evolutionary aspects of plastid chromosome architecture in land plants and their putative ancestors. We provide an overview on the structure and composition of the plastid genome of land plants as well as the functions of its genes in an explicit phylogenetic and evolutionary context. We will discuss the architecture of land plant plastid chromosomes, including gene content and synteny across land plants. Moreover, we will explore the functions and roles of plastid encoded genes in metabolism and their evolutionary importance regarding gene retention and conservation. We suggest that the slow mode at which the plastome typically evolves is likely to be influenced by a combination of different molecular mechanisms. These include the organization of plastid genes in operons, the usually uniparental mode of plastid inheritance, the activity of highly effective repair mechanisms as well as the rarity of plastid fusion. Nevertheless, structurally rearranged plastomes can be found in several unrelated lineages (e.g. ferns, Pinaceae, multiple angiosperm families). Rearrangements and gene losses seem to correlate with an unusual mode of plastid transmission, abundance of repeats, or a heterotrophic lifestyle (parasites or myco-heterotrophs). While only a few functional gene gains and more frequent gene losses have been inferred for land plants, the plastid Ndh complex is one example of multiple independent gene losses and will be discussed in detail. Patterns of ndh-gene loss and functional analyses indicate that these losses are usually found in plant groups with a certain degree of heterotrophy, might rendering plastid encoded Ndh1 subunits dispensable

The Deletion of Vittaria graminifolia from the Flora of Florida

Volume: 70Start Page: 12End Page: 1

Chromosome Numbers in the Fern Genus Anogramma, II

Volume: 68Start Page: 3End Page:

Phylogeny and Generic Circumscriptions of Cheilanthoid Ferns (Pteridaceae: Cheilanthoideae) Inferred from rbcL Nucleotide Sequences

Volume: 85Start Page: 341End Page: 36

Species Concepts in Pteridophytes: The Treatment and Definition of Agamosporous Species

Volume: 79Start Page: 65End Page: 7

Phylogenetic Placements of Loxoscaphe thecifera (Aspleniaceae) and Actiniopteris radiata (Pteridaceae) Based on Analysis of rbcL Nucleotide Sequences

Volume: 91Start Page: 197End Page: 21

Obituary: Rolla Milton Tryon, Jr. (1916–2001)

Volume: 92Start Page: 1End Page:

Obituary: Alice Faber Tryon (1920–2009)

Volume: 99Start Page: 231End Page: 23

Characterization of Four Members of the Alpha-Tubulin Gene Family in Ceratopteris richardii

Volume: 97Start Page: 47End Page: 6