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 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.

The Evolutionary Dynamics of Apomixis in Ferns: A Case Study from Polystichoid Ferns

“…In this lineage we did not find a correlation between speciation/extinction rates and apomixis (see results of BiSSE analyses). Nevertheless, the analyses of the polystichoid dataset did support the hypothesised association of apomixis and reticulate evolution involving polyploidy [5,17,[20][21][22][23]. The main caveat here is that polyploidy alone is insufficient to confirm reticulation because chromosome numbers do not provide sufficient evidence to distinguish between auto-and allopolyploidy.…”

“…The SE Asian monsoon hypothesis is consistent with some other observations of apomictic ferns. Apomixis is especially common among the xerophytic cheilanthoid ferns [17,[20][21][22]. Apomictic species of Aspleniaceae occur preferably in areas with season rainfalls such as parts of Africa, for example, Asplenium aethiopicum complex, and northern Central America, for example, Asplenium monanthes complex [9,10].…”

“…Polyploidy and reticulate evolution are strongly linked with the occurrence and establishment of apomixis in both ferns and angiosperms [5,[17][18][19][20][21][22][23]. This link is especially true for triploid and pentaploid taxa [13,19,23].…”

Dehydration protection provided by a maternal cuticle improves offspring fitness in the moss Funaria hygrometrica

“…Of these structures, the plant cuticle is ubiquitous, occurring in taxa from all major lineages of land plants [e.g. mosses (Proctor, 1979), cheilanthoid ferns (Sigel et al, 2011), gymnosperms, Ginkgo (Taylor et al, 1989) and angiosperms, Agave (Wattendorff and Holloway, 1980)]. The cuticle consists of layers of the biopolymers cutin/cutan and waxes that cover and permeate the outermost layers of the cell wall (Holloway, 1982), decreasing intracellular water loss.…”

Fase gametofítica de las tres variedades de Argyrochosma nivea (Pteridaceae).

“…Sigel et al (2011) al estudiar las relaciones filogenéticas de las especies con farinas, encuentran que la farina del género Argyrochosma surgió de manera independiente de la farina de las especies del género Notholaena.…”