Evaluating the status of fern and lycophyte nothotaxa in the context of the Pteridophyte Phylogeny Group classification (PPG I)

Abstract

Hybridization has long been recognized as common in ferns, but the products of this arguably evolutionary important process have often been ignored in classifications. For example, the recently published Pteridophyte Phylogeny Group classification (PPG I) covered all hierarchical ranks from class to genus but did not include intergeneric hybrids (nothogenera). Here, we provide for the first time a comprehensive evaluation of previously proposed nothogenera in the context of a current phylogeny-based pteridophyte classification (i.e., PPG I). We find that several nothogenera nested in the orders Osmundales and Polypodiales are supported in the framework of PPG I, but others are superfluous. Five new nothogenera are introduced here for the first time. We also explore the distribution of nothospecies across the pteridophyte phylogeny for the first time. We are unable to reject the hypothesis that species richness and nothospecies diversity are correlated, despite the finding that some temperate lineages contribute more nothospecies than expected whereas several tropical lineages lack them. This pattern could be the consequence of either fundamental differences in modes of speciation in temperate and tropical zones or unequal efforts to record nothospecies. In general, we emphasize the need to take nothogenera into account when proposing generic classifications, but the information provided by the existence of such hybrids needs to be carefully evaluated. Our results underscore the need to report and study hybrids in ferns and lycophytes, especially in biodiversity rich areas.

An open and continuously updated fern tree of life

“…Furthermore, multiple genera included in PPG I were known to be non-monophyletic and provisionally circumscribed ( Pteridophyte Phylogeny Group I, 2016 ). pteridocat includes newly published genera, some genera that were not recognized by PPG I, and nothogenera, which were not included in PPG I ( Liu et al, 2020 ). Differences between pteridocat and PPG I are summarized in Supplementary Table 1 .…”

Hybphaser identifies hybrid evolution in Australian Thelypterid ferns

“…Russell River Fern is the first genetically confirmed inter-generic fern hybrid recorded for Australia. Hybridisation between genera is known to occur occasionally in ferns, and Liu et al (2020) list twelve confirmed and three possible nothogenera in ferns and lycophytes. A fern nothogenus between genera that diverged 60 million years ago is the most extreme example known (Rothfels et al, 2015).…”

“…There is a growing body of research revealing that hybridization is also an important contributor to speciation, and that it may be more common than previously known (Mallet, 2007; Soltis & Soltis, 2009; Abbott et al, 2013; Vaux et al, 2016; Kinosian et al, 2020; Nauheimer et al, 2020; Requena et al, 2020, Rutherford 2020; Ottenburghs, 2020). A reticulate evolutionary history may be important for generation of future diversification and a key to the successful radiation of some groups (Goulet et al, 2017; Liu et al, 2020; Requena et al, 2020). Hybrid speciation and introgression may be an important reason evolutionary relationships have been difficult to resolve using phylogeny in some groups of plants (Mallet et al, 2016).…”

An Open and Continuously Updated Fern Tree of Life

“…Furthermore, multiple genera included in PPG I were known to be non-monophyletic and provisionally circumscribed (Pteridophyte Phylogeny Group I, 2016). Pteridocat includes newly published genera, some genera that were not recognized by PPG I, as well as nothogenera, which were not included in PPG I (Liu et al, 2020). Differences between pteridocat and PPG I are summarized in Table S1.…”