Recognition of Gastoniella (Pteridoideae, Pteridaceae) [PASSED]

[liangfern]

Author(s) of proposal

Liang Zhang

Name of taxon

Gastoniella

Rank of taxon

Genus

Approximate number of species affected

3

Description of change

Zhang et al . (2017) resolved the subfamily Pteridoideae into four strongly supported monophyletic clades: the Pteris clade, the Actiniopteris + Onychium clade, the JAPSTT clade (Jamesonia, Austrogramme, Pterozonium, Syngramma, Taenitis, Tryonia), and the GAPCC (Gastoniella, Anogramma, Pityrogramma, Cerosora, Cosentinia) clade. Within the GAPCC clade, Gastoniella is proposed as a new genus segregated from Anogramma in order to maintain monophyletic Anogramma s.s. and Pityrogramma s.s.

Reason for change

Instead of recognize six genera in the GAPCC clade, one might argue that the four genera, Anogramma, Cerosora, Cosentinia, and Gastoniella can all be synonymized under Pityrogramma s.l. given that: (1) the monophyly of Pityrogramma s.l. is strongly supported; and (2) except Cosentinia, most species of the other three genera have already been placed in Pityrogramma by Domin (1928), e.g., P. chaerophylla, P. leptophylla, and P. microphylla. However, we advocate for the acceptance of these five strongly supported lineages as five genera for the following reasons: (1) They have distinct distributions with Cerosora and Cosentinia being the Old World genera, Pityrogramma and Gastoniella being the New World genera, and Anogramma having worldwide distribution; (2) There are abundant molecular variations among the five genera (e.g., 74-bp divergence exists between Gastoniella chaerophylla and P. calomelanos in 1262 bps of the rbcL gene alone); (3) The monophyly of each genus is strongly supported in molecular analyses; (4) The four genera each have anomalous morphology comparing with Pityrogramma s.s (see below); and (5) Most names have been available for other four genera.

Morphologically, the new genus Gastoniella differs from Cosentinia by having glabrous fronds, ovate-deltoid laminae; from Anogramma by having linear ultimate segments; from Pityrogramma by having annual and smaller habit of the sporophytes and no farina; from Cerosora by having linear ultimate segments, tufted rhizome (C. microphylla) or no farina (C. argentea).

Reference(s) for publication of the name

Domin, K., 1928. Generis Pityrogramma (Link) species ac sectiones in clavem analyticam dispositae. Spisy Vyd. Pøirod. Fak. Karlovy Univ. (Publ. Fac. Sci. Charles Univ.), 88, 1–10.
https://biotanz.landcareresearch.co.nz/references/d2c32d1f-9835-4566-b85c-eaf51fef44dd

Zhang, L., Zhou, X.-M., Lu, N.T., Zhang, L.-B., 2017. Phylogeny of the fern subfamily Pteridoideae (Pteridaceae; Pteridophyta), with the description of a new genus: Gastoniella. Mol. Phylogenet. Evol. 109, 59–72.
https://doi.org/10.1016/j.ympev.2016.12.037

List the numbers of any related issues

No response

Code of Conduct

• I agree to follow the PPG Code of Conduct

[gyatskievych]

I think that recognition of Gastoniella by PPG is premature. The proposal does not cite the foundational work upon which phylogenetic study of this group was based: Nakazato, T., Gastony, G.J., 2003. Molecular phylogenetics of Anogramma species and related genera (Pteridaceae: Taenitidoideae). Syst. Bot. 28, 490–502. In that earlier work, which was based on data only from rbcL sequences, the authors chose not to segregate the Anogramma chaerophylla complex, stating: "Pityrogramma sulphurea and several other species of that genus, unavailable for this study, were specifically cited by R. Tryon (1962) as morphologically closest to Anogramma. Where rbcL would place those Pityrogramma species relative to the Anogramma clades of Fig. 5 remains to be determined." The Zhang et al. (2017) study increased the number of molecular markers, but failed to address the issue of incomplete critical taxon sampling for Pityrogramma. Additionally, that study had relatively high amounts of incomplete sequence data in its matrix. Thus, formal taxonomic segregation of Gastoniella was likely premature. There have been no subsequent studies to flesh out the branching pattern, so I view this as an unresolved issue.

[crothfels]

I'm not super familiar with this group, and others may know better (@msundue @westesto -- aside -- is there a way to know what people's handles are, so we can tag them?). But based on the Zhang et al 2017 tree, Gastoniella isn't congeneric with Pityrogramma (unless Cerosora also is) and isn't congeneric with Anogramma (unless the whole GAPCC clade is treated as Pityrogramma). So while I recognize @gyatskievych 's point, I think the recognition of Gastoniella is warranted. We may discover that other species fall in the genus, but we're "stuck" recognizing it unless we want to sink Cerosora, basically.

[joelnitta]

@crothfels thanks for the aside. I started a Discussion about it, so please post additional comments there.

[joelnitta]

This proposal was voted on during PPG Ballot 8 (voting period February 2024). A total of 70 votes were cast. There were 49 'Yes' votes (70%) and 21 'No' votes (30%). The proposal passes.