The Neotropical genus Jamesonia Hook. & Grev. sensu stricto is among the most distinctive of all fern genera. It has linear, indeterminate leaves bearing highly reduced, coriaceous pinnae covered with dense pubescence (Tryon 1962; Fig. 1). These morphological characteristics are generally considered to be an adaptation to the high-elevation Andean páramo habitats where most Jamesonia species reside (Tryon et al. 1990). Based on reproductive and other cryptic morphological characteristics, Jamesonia has long been thought to be closely related to the genus Eriosorus Fée (Tryon 1962, 1970, Tryon and Tryon 1982). Eriosorus mostly occupies middle-elevation habitats in the Andes and its leaves are much more typical of ferns, usually being very dissected and rather delicate in texture (Tryon 1970; Figs 2, 3). Recent analyses have demonstrated that Jamesonia is both nested within Eriosorus and polyphyletic (Prado et al. 2007, Sánchez-Baracaldo 2004a, 2004b, Schneider et al. 2013, Schuettpelz et al. 2007), supporting the hypothesis of Tryon (1962, 1970) that the unique morphology of Jamesonia evolved independently multiple times. This finding prompted the recent recombination of all known species of Eriosorus into Jamesonia (sensu lato, Christenhusz et al. 2011).

Although it is clear that species of Jamesonia sensu stricto are intermixed with those previously assigned to Eriosorus, relationships remain rather poorly supported and additional studies are needed to better resolve the evolutionary history of this group. With that said, the isolated phylogenetic position revealed for one Brazilian species requires special attention. In the most comprehensive study of Jamesonia sensu lato to date (Sánchez-Baracaldo 2004b), two accessions of Eriosorus myriophyllus (Sw.) Copel. (Fig. 4) were resolved together and well supported as sister to the remainder of Jamesonia sensu lato. However, it is clear from the phylogram included in the Sánchez-Baracaldo (2004b) study that these accessions are genetically more similar to the outgroup used than they are to the remainder of the ingroup, suggesting that the phylogenetic position of Eriosorus myriophyllus may be an artifact of including a single outgroup genus (Pterozonium Fée). Subsequent analyses with a broader phylogenetic context but including fewer exemplars from within Jamesonia sensu lato, actually found Eriosorus myriophyllus to be most closely related to the genus Taenitis Willd. ex Schkuhr (Prado et al. 2007, Schneider et al. 2013).

Here, through analyses of a four-gene (atpA, chlL, rbcL, and rps4) plastid dataset that incorporates many Eriosorus and Jamesonia sensu stricto species, as well as a broad sampling of related genera, we aim to better resolve the phylogenetic position of Eriosorus myriophyllus and allied species. Based on our results, we describe a new genus, Tryonia Schuettp., J.Prado & A.T.Cochran, to accommodate this species and its closest allies.

The four single-gene (atpA, chlL, rbcL, and rps4) datasets contained varying amounts of phylogenetic signal, providing significant support (Bayesian posterior probability, BPP ≥ 0.95) for as few as 11 and as many as 17 bipartitions (Table 3). The single-gene trees were largely consistent in their resolved relationships (trees not shown) and there were no well-supported (BPP ≥ 0.95) conflicts among them.

Our combined four-gene dataset comprised a total of 4514 characters, of which 660 were variable (Table 3). Analysis of this dataset resulted in a phylogeny with considerably improved support relative to the single-gene phylogenies; 25 bipartitions had a BPP ≥ 0.95 (Fig. 5). The separation of Actiniopteris and Onychium from the remaining taenitidoid genera was well supported (BPP = 1.00). Anogramma, Cosentinia, and Pityrogramma formed a well-supported clade that was, in turn, well-supported as sister to a robust clade including Austrogramme, Pterozonium, Syngramma, Taenitis, and all sampled species previously assigned to either Jamesonia or Eriosorus (Fig. 5).

The vast majority of our Jamesonia sensu lato collections come together in a clade on a rather long branch; within this clade branches are short and support is frequently lacking. Six samples previously included within Jamesonia sensu lato are not allied to that larger clade, but rather are embedded within a well-supported clade that also contains Austrogramme, Pterozonium, Syngramma, and Taenitis (Fig. 5).

Most species previously assigned to Eriosorus and Jamesonia sensu stricto have been consistently resolved together in a well-supported clade (Prado et al. 2007, Sánchez-Baracaldo 2004a, 2004b, Schneider et al. 2013, Schuettpelz et al. 2007). And, although support for relationships within this large clade has been generally lacking, the hypothesis that Jamesonia sensu stricto was derived from within Eriosorus (Tryon 1962, 1970) has received considerable backing. In our combined analysis, we too find strong support for a clade containing most sampled Eriosorus and Jamesonia sensu stricto species (Fig. 5). Additionally, we find strong support for some of its constituent internal nodes, which indicate that neither Eriosorus nor Jamesonia sensu stricto is monophyletic. Phylogenetic analyses incorporating a more comprehensive sample of taxa and a greater number of markers will ultimately be necessary to fully understand evolutionary relationships within this clade. However, based solely on the evidence to date, it is abundantly clear that Jamesonia and Eriosorus (as typically circumscribed) cannot both be recognized, assuming monophyly as a criterion for generic delimitation. With Jamesonia being the older name (published in 1830, versus 1852 for Eriosorus), the recombination of all known species of Eriosorus into Jamesonia in Christenhusz et al. (2011) was mostly warranted.

Eriosorus myriophyllus was shown by Prado et al. (2007), Sánchez-Baracaldo (2004b), and Schneider et al. (2013) to be isolated relative to most other species previously assigned to Eriosorus or Jamesonia sensu stricto. Here, we find Eriosorus myriophyllus and two previously unsampled species of Eriosorus to be more closely related to Austrogramme, Pterozonium, Syngramma, and Taenitis than to Jamesonia (as newly circumscribed herein, Fig. 5). Support for this relationship is strong (BPP = 1.00) and the implications are significant if monophyly is used as a criterion for generic delimitation. Because the type of Jamesonia (Jamesonia pulchra Hook. & Grev.) is resolved well within the large Jamesonia clade and the type of Eriosorus (Eriosorus aureonitens (Hook.) Copel.) shows clear morphological and geographical affinities to this clade, and because there are no other generic names available for the Eriosorus myriophyllus group, we here describe a new genus—Tryonia (see below)—to accommodate the isolated species.

In her monograph of Eriosorus, Tryon (1970) identified several small groups of closely allied species. Among these was the species pair of Eriosorus myriophyllus and Eriosorus sellowianus (with Eriosorus schwackeanus considered by her to be a synonym ofEriosorus sellowianus). This group corresponds perfectly to our proposed circumscription of Tryonia. We find Eriosorus myriophyllus, Eriosorus schwackeanus (which we consider to be distinct from Eriosorus sellowianus), and the recently described Eriosorus areniticola (Schwartsburd and Labiak 2008) to form a genetically isolated clade of closely related species (Fig. 5). New combinations for these species, along with the unsampled Eriosorus sellowianus, are provided below.

Based on our current dataset, we do not consider the precise phylogenetic position of Tryonia (within the Austrogramme, Pterozonium, Syngramma, Taenitis, and Tryonia clade) to be fully resolved. Although our combined analysis clearly places Tryonia sister to Austrogramme, Syngramma, and Taenitis (collectively), this relationship is not well supported in any single-gene analysis. The atpA and rbcL datasets do place Tryonia sister to Taenitis (atpA and rbcL sequences were not available for Austrogramme and Syngramma), but support is lacking (BPP = 0.61 and 0.83, respectively). Likewise, the rps4 dataset resolves Tryonia as sister to Austrogramme, Syngramma, and Taenitis without significant support (BPP = 0.88). Strong single-gene support for the precise position of Tryonia only comes from the chlL dataset, where Tryonia is most closely related to Pterozonium (BPP = 1.00).

Two of the species of Tryonia included in our phylogenetic analysis (Tryonia areniticola and Tryonia schwackeana) are endemic to Brazil; the third sampled species (Tryonia myriophylla) also occurs in Uruguay, near its border with the Brazilian state of Rio Grande do Sul. Although the Andes are the center of diversity for Jamesonia (as newly circumscribed herein), this genus is not entirely geographically distinct from Tryonia. In the recently published Catálogo de Plantas e Fungos do Brasil, a total of nine species are ascribed to Eriosorus or Jamesonia (Prado 2010). Only three of these species noted for Brazil (Eriosorus areniticola, Eriosorus myriophyllus, and Eriosorus schwackeanus) are resolved as sister to Austrogramme, Syngramma, and Taenitis. We found Eriosorus cheilanthoides, Eriosorus insignis, and Jamesonia brasiliensis to be embedded within the Jamesonia clade (Fig. 5) and Eriosorus rufescens was resolved within Jamesonia in an earlier study (Sánchez-Baracaldo 2004b). As for the remaining Brazilian species that have yet to be included in a phylogenetic study, one (Eriosorus sellowianus) shows clear morphological affinities to, and is here considered to be a member of, Tryonia; the other (Eriosorus biardii) appears, based on morphology, to be best accommodated in Jamesonia. Regardless of the ultimate phylogenetic placement of these two unsampled species, the genus Tryonia can be described as wholly endemic to Brazil and Uruguay.