Ynesmexia: A novel genus uniting morphologically disparate cheilanthoid ferns (Pteridaceae)

Here we focus on the “skinneri clade” of cheilanthoid ferns (Pteridaceae), revising its taxonomy based on a new set of molecular, cytogenetic, and morphological analyses. Though previously assigned to disparate genera, the five taxa formally recognized in this clade form a strongly supported monophyletic group when analyzed with both plastid (rbcL, atpA, trnG-R) and nuclear (gapCp) datasets. This novel lineage is recognized here as Ynesmexia gen. nov. in honor of Ynés Mexía, a pioneering Mexican-American botanist. Our molecular analyses indicate that Ynesmexia comprises two monophyletic groups, referred to here as the “subcordata” and “seemannii” subclades. The “subcordata” subclade encompasses plants previously treated as Cheilanthes skinneri, ×Hemionanthes gryphus and Hemionitis subcordata. Our data indicate that the first taxon comprises two species: a diploid treated here as Ynesmexia fournieri (comb. nov.) and a tetraploid corresponding to Y. skinneri (comb. nov.) s.str. Amplifying the differences in ploidy, these two taxa are distinguished by several aspects of sporophyte morphology, non-overlapping spore sizes, and allopatric geographic distributions. Our analyses also highlight the role of hybridization and polyploidy in the evolution of the group, indicating that: (1) Y. ×gryphus (comb. nov.) is a largely fertile homoploid hybrid between Y. subcordata (comb. nov.) and Y. fournieri, and (2) Y. skinneri s.str. is an allotetraploid between members of the “subcordata” and “seemannii” subclades. Although the latter subclade is morphologically (and likely cytogenetically) diverse, current data are insufficient to propose formal subdivision of the only recognized species, Y. seemannii (comb. nov.). The findings presented here challenge earlier taxonomic frameworks and offer new insights into the evolutionary history of this xeric-adapted fern lineage, underscoring the importance of using multi-faceted approaches to resolve complex taxonomic issues in plant biology.

Duke Scholars

Author Kathleen M. Pryer Biology