George Yatskievych

A community-derived classification for extant lycophytes and ferns

Phylogeny has long informed pteridophyte classification. As our ability to infer evolutionary trees has improved, classifications aimed at recognizing natural groups have become increasingly predictive and stable. Here, we provide a modern, comprehensive classification for lycophytes and ferns, down to the genus level, utilizing a community‐based approach. We use monophyly as the primary criterion for the recognition of taxa, but also aim to preserve existing taxa and circumscriptions that are both widely accepted and consistent with our understanding of pteridophyte phylogeny. In total, this classification treats an estimated 11 916 species in 337 genera, 51 families, 14 orders, and two classes. This classification is not intended as the final word on lycophyte and fern taxonomy, but rather a summary statement of current hypotheses, derived from the best available data and shaped by those most familiar with the plants in question. We hope that it will serve as a resource for those wanting references to the recent literature on pteridophyte phylogeny and classification, a framework for guiding future investigations, and a stimulus to further discourse.

A Diploids-First Approach to Species Delimitation and Interpreting Polyploid Evolution in the Fern Genus Astrolepis (Pteridaceae)

Abstract Polyploidy presents a challenge to those wishing to delimit the species within a group and reconstruct the phylogenetic relationships among these taxa. A clear understanding of the tree-like relationships among the diploid species can provide a framework upon which to reconstruct the reticulate events that gave rise to the polyploid lineages. In this study we apply this “diploids-first” strategy to the fern genus Astrolepis (Pteridaceae). Diploids are identified using the number of spores per sporangium and spore size. Analyses of plastid and low-copy nuclear sequence data provide well-supported estimates of phylogenetic relationships, including strong evidence for two morphologically distinctive diploid lineages not recognized in recent treatments. One of these corresponds to the type of Notholaena deltoidea, a species that has not been recognized in any modern treatment of Astrolepis. This species is resurrected here as the new combination Astrolepis deltoidea . The second novel lineage is that of a diploid initially hypothesized to exist by molecular and morphological characteristics of several established Astrolepis allopolyploids. This previously missing diploid species is described here as Astrolepis obscura.

Species Relationships and Farina Evolution in the Cheilanthoid Fern Genus Argyrochosma (Pteridaceae)

Abstract 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 homoplastic characters, to define major 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 the circumscription 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 group, there has been at least one evolutionary reversal (loss) of farina and the development of major chemical variants that 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 evolution and suggests the presence of several previously undetected taxa of Argyrochosma.

Chromosome studies of cheilanthoid ferns (Pteridaceae: Cheilanthoideae) from the western United States and Mexico

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.

A global plastid phylogeny of the brake fern genus Pteris (Pteridaceae) and related genera in the Pteridoideae

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.

Exudate Flavonoids in Asteraceae from Arizona, California and Mexico

Abstract A series of Asteraceae, belonging to the tribes Astereae, Eupatorieae, Helenieae and Heliantheae, have been analyzed for the presence of flavonoid aglycones accumulated on leaf and stem surfaces. Methyl ethers of apigenin, luteolin, kaempferol, and quercetin as well as methyl ethers of their relevant 6 -hydroxy derivatives were abundant, whereas 8 -O-substi-tuted derivatives and flavanones were encountered only occasionally; 6 ,8 -di-O-substituted flavonols were found in only one species.

External leaf flavonoids of Polanisia trachysperma

Abstract Polanisia trachysperma , a sticky annual weed, produces a terpenoid leaf resin. This exudate is shown to contain more than a dozen methylated flavonoid aglycones, some of which are rare natural products. Compounds with 6,8-dimethoxy substitution are predominant. Polanysia trachysperma is the first Capparaceae species found to accumulate external flavonoids.

Chloroplast DNA evolution and phylogeny of some polystichoid ferns

Restriction site mutations in the chloroplast DNAs from members of the fern genus, Phanerophlebia, and some representatives of Cyrtomium and Polystichum were used to elucidate phylogenetic relationships within and between these groups. Evidence is presented against the hypothesis that Phanerophlebia was derived from Cyrtomium; rather the two genera appear to be convergent segregate genera that arose independently from Polystichum. The chloroplast DNA mutations also provide information on the maternal parentage of several tetraploid species

A New Species And Three Generic Transfers In The Fern Genus Notholaena (pteridaceae)

ABSTRACT Three species of farinose ferns traditionally included in the large, polymorphic genus Cheilanthes Swartz are transferred to the genus Notholaena R. Brown as N. aureolina Yatskievych & Arbeláez, N. jaliscana Yatskievych & Arbeláez, and N. ochracea (Hooker) Yatskievych & Arbeláez. Additionally, a Central American novelty is described as a new species, N. montielae Yatskievych & Arbeláez, with a type from Nicaragua.

A New Genus of Holoparasitic Orobanchaceae from Mexico

Abstract We describe here a novel achlorophyllous parasite on the roots of Hedyosmum mexicanum C. Cordemoy (Chloranthaceae) as a new genus and species, Eremitilla mexicana Yatskievych & J. L. Contreras. The new taxon is currently thought to be endemic to the state of Guerrero, Mexico. It is best classified in the Orobanchaceae, but differs from other members of the family in having 5-ribbed, muricate ovaries containing five parietal placentae, as well as unusual stamens in which the anther is partially embedded in an expanded filament apex. Within the Orobanchaceae, the new taxon is probably related to a group that contains the other American holoparasitic genera. Morphologically, Eremitilla Yatskievych & J. L. Contreras displays a number of autapomorphies, but few identifiable synapomorphies. This presumed relictual taxon presently is known only from a restricted habitat and a very small geographic range, and thus is of conservation concern.