Major evolutionary events in the origin and diversification of the fern genus Polystichum (Dryopteridaceae)

Abstract

Recent advances in molecular systematics of the ferns make it possible to address long-standing questions about classification of the major fern genera, such as the worldwide genus Polystichum (Dryopteridaceae), comprising at least 200 species. In this study we examined rbcL sequences and morphological characters from 55 fern taxa: 34 were from Polystichum and 21 were from other genera in the Dryopteridaceae. We found that Phanerophlebia, possibly including Polystichopsis, is the sister group to Polystichum sensu lato (s.l.), including Cyrtomium. Polystichum as commonly recognized is paraphyletic. Our results lead us to suggest recognizing the clade of earliest diverging Polystichum species as a distinct genus (Cyrtomidictyum) and to continue to recognize Cyrtomium as a separate genus, leaving a monophyletic Polystichum sensu stricto (s.s.). We resolved a tropical American clade and an African clade within Polystichum s.s. However, the resemblance between the once-pinnate, bulb-bearing calciphilic species found in Asia and the West Indies appears to be the result of convergent evolution. Optimizing our morphological character transformations onto the combined phylogeny suggests that the common ancestor of Polystichum s.l. and Phanerophlebia had evolved the common features of the alliance, including ciliate petiole-base scales, once-pinnate fronds, ultimate segments with scarious tips, peltate indusia, and microscales.

A well-sampled phylogenetic analysis of the polystichoid ferns (Dryopteridaceae) suggests a complex biogeographical history involving both boreotropical migrations and recent transoceanic dispersals

“…Indeed, this genus is divided into two well-supported lineages, ranked as subgenera by Zhang and Barrington (2013a). The sister relationship between these two lineages is only weakly supported, but is consistent with previous molecular (e.g., Driscoll and Barrington, 2007;Li et al, 2007Li et al, , 2008Little and Barrington, 2003) and morphological studies (Zhang and Barrington, 2013a). The uncertainty around the phylogenetic position of the Polystichum subgenera does, however, not influence the result of our biogeographical analysis.…”

“…By extending the sampling, we have been able to reconstruct a worldwide, time-calibrated phylogeny for this large group of ferns. Phylogenetic relationships are generally congruent with previous studies (Driscoll and Barrington, 2007;Little and Barrington, 2003;Lu et al, 2007;McHenry and Barrington, 2014). However, the monophyly of Polystichum still remains unresolved.…”

“…A more detailed analysis of these genera will be published separately. Based on previous molecular (e.g., Little and Barrington, 2003;Li et al, 2004Li et al, , 2008Driscoll and Barrington, 2007;Schuettpelz and Pryer, 2007;Lu et al, 2007;Liu et al, 2007) and morphological studies (Smith et al, 2006;Zhang et al, 2013), four species of Elaphoglossum Schott, two of Mickelia R.C. Moran, Labiak & Sundue, one of Bolbitis Schott, eight of Dryopteris Adans., four of Arachniodes Blume, and two of Polystichopsis (J.…”

“…In this study, we focus on the polystichoid ferns (Driscoll and Barrington, 2007;Little and Barrington, 2003;Schuettpelz and Pryer, 2007), namely Cyrtomium C. Presl, Phanerophlebia C. Presl, and Polystichum Roth (sensu Zhang, 2012;Zhang and Barrington, 2013a)., Polystichum is one of the most diverse fern genera, with about 500 species distributed worldwide but more common in temperate and subtropical regions (Zhang and Barrington, 2013a). The highest diversity is undoubtedly found in East Asia (e.g., 208 spp.…”

“…The monophyly of polystichoid ferns is not in doubt (Driscoll and Barrington, 2007;Li et al, 2007;Little and Barrington, 2003;Lu et al, 2007;Schuettpelz and Pryer, 2008;McHenry and Barrington, 2014;Le Péchon et al, 2016) and unlike most other fern taxa, Polystichum has been a subject of several previous biogeographical analyses (e.g., Perrie et al, 2003;Li et al, 2004Li et al, , 2007Driscoll and Barrington, 2007;McHenry and Barrington, 2014). Polystichum may have originated in (i) Asia ca.…”