Proposal to recognize Aenigmatogrammitis, Boonkerdia, Grammitastrum, Howeogrammitis, Nanogrammitis, Oxygrammitis, Rouhania, and Thalassogrammitis (Grammitidoideae, Polypodiaceae) [PASSED]

[msundue]

Author(s) of proposal

Michael Sundue, Barbara Parris, LiBing Zhang

Name of taxon

Aenigmatogrammitis, Boonkerdia, Grammitastrum, Howeogrammitis, Nanogrammitis, Oxygrammitis, Rouhania, Thalassogrammitis

Rank of taxon

Genus

Approximate number of species affected

25

Description of change

Proposal to recognize Aenigmatogrammitis, Boonkerdia, Grammitastrum, Howeogrammitis, Nanogrammitis, Oxygrammitis, Rouhania, and Thalassogrammitis

Reason for change

Recent phylogenetic analyses have called into question the circumscription of Grammitis, Oreogrammitis, Prosaptia and Ctenopterella, and the following seven genera have been described as part of the taxonomic solution. These include Aenigmatogrammitis, Boonkerdia, Grammitastrum, Howeogrammitis, Nanogrammitis, Oxygrammitis, Rouhania, and Thalassogrammitis. While this is a large increase in genera housing a relatively small number of species (~25), Zhou et al. (2023) argued that recognizing these clades as genera is more congruent with their morphology and geography of the clades, and that the alternate solution of lumping them into available genera would undermine the coherence of the previously described genera.

It can also be said that the solutions proposed by Zhou et al. (2023) were not made in isolation but were the result of communication between many of the researchers actively working on grammitid fern systematics, signaling strong support for the recognition of these genera from that taxonomic community. Moreover, an earlier proposal (#72) related to this one to recognize Devolia, Calligrammitis, and Glabrigrammitis, passed in April 2024 (PPG Ballot #10).

Aenigmatogrammitis (endemic to Australia) and Oxygrammitis (Malesia) contain species that have been treated in Grammitis and Ctenopterella respectively. The former is sister to a clade containing Oxygrammitis and Acrosorus (Asia-Pacific), a relationship also found in earlier studies (Sundue et al. 2014; Bauret et al. 2017). These three genera were monophyletic in Zhou et al. (2023), and could potentially be united into a single genus, but given their morphological disparity, Zhou et al. (2023) concluded that treating them as distinct would be more appropriate. Grammitastrum, Howeogrammitis, and Thalassogrammitis contain species that have been residing in Grammitis pending a taxonomic solution to the polyphyly of species in that genus. These three genera formed a strongly supported clade in Zhou et al. (2023), and could potentially be united into a single genus, but Zhou et al. (2023) suggest that because they are so morphologically distinct, treating them as three genera would be most appropriate. Moreover, there are no obvious morphological characters to define the clade formed by the three.

Howeogrammitis is endemic to Lord Howe Island, whereas the other two genera are endemic to New Caledonia. These three genera together are weakly to strongly supported as sister to Notogrammitis and the four together are sister to Ctenopterella s.str. These phylogenetic results were found by earlier studies as well, (Sundue & al., 2014; Bauret & al., 2017).

Species of Nanogrammitis and Rouhania are distributed in Africa and West Indian Ocean islands and contain species that were residing in Grammitis and Ctenopterella respectively. These two genera have been found sister to each other in phylogenetic analyses (Sundue & al., 2014; Bauret & al., 2017; our Fig. 1). All species of Nanogrammitis have simple laminae like those of Grammitis s.str., while all except two of Rouhania have pinnatisect laminae like those of Ctenopterella s.str. Considering their disparate morphology, Zhou et al. (2023) recognized them as distinct explaining that “It seems better to treat the two simple-fronded Grammitis pygmaea and G. nanodes in a Ctenopterella-dominant (pinnatisect-fronded) genus than to treat 6+ pinnatisect-fronded species of Ctenopterella in a simple-fronded genus”.

Following Zhou et al. (2023), the polyphyly of Ctenopterella sensu Parris (2007) is resolved by recognizing four genera: Ctenopterella s.str. (the C. lasiostipes clade), Boonkerdia gen. nov. (C. khaoluangensis), Oxygrammitis gen. nov. (C. denticulata), and Rouhania gen. nov. (the C. zenkeri clade + Grammitis pygmaea and G. nanodes). Boonkerdia differs from Ctenopterella s.str. in lacking setae and branched hairs with setae as branches. Boonkerdia is be distinguished from Tomophyllum by having a dorsiventral rather than a radial rhizome and in lacking setae. Oxygrammitis differs from Ctenopterella s.str. in having the lamina bipinnately to tripinnately divided, with the ultimate divisions of the lamina apically acute to acuminate. Rouhania is quite similar to Ctenopterella morphologically, but the two differs in geographical and are not phylogenetically close to each other. Although Boonkerdia, Devolia, and Tomophyllum form a clade together, Zhou et al. (2023) argue that they should not be combined; the clade has low support (<50%/<0.5), and the lineages are morphologically disparate.

Alternate proposal

Oxygrammitis could be combined with Aenigmatogrammitis into Acrosorus, but these are morphologically aberrant plants and the genus would not be easily diagnosed.

Howeogrammitis, Thalassogrammitis, and Grammitastrum could be combined into Notogrammitis, but these are morphologically aberrant groups and the genus would not be easily diagnosed.

Boonkerdia could be combined with Devolia into Tomophyllum but these are morphologically aberrant groups and the genus would not be easily diagnosed.

Rouhania and Nanogrammitis could be combined but these are morphologically aberrant groups and the genus would not be easily diagnosed.

Reference(s) for publication of the name

Zhou, X.M., Yang, J.J., Liang, Z.L., Pollawatn, R., Knapp, R., Parris, B., Sundue, M., Ranker, T.A., Zhou, L., Lu, N.T. and Luong, T.T., 2023. A global phylogeny of grammitid ferns (Polypodiaceae) and its systematic implications. Taxon, 72(5), pp.974-1018.

TAXON - 2023 - Zhou - A global phylogeny of grammitid ferns Polypodiaceae and its systematic implications (3).pdf

Grammitids tree.pdf

List the numbers of any related issues

72

Code of Conduct

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[joelnitta]

@msundue do you mind editing your proposal to be actual text instead of an image of text? It is difficult to read on my screen, and may be for others as well. Thanks!

[msundue]

Done. Let me know if anything is still not clear.

[joelnitta]

Thanks!

[SchneiderHarald]

This proposal continues to cleaning process to adjust the generic classification of these ferns to reflect the most recent phylogenetic hypotheses and already accepted genera. It is therefore consistent with previous decisions despite the trend towards a high number of relative species poor genera is a bit worrying.

[htuom]

I would like to take a step back here and question whether we really need so many genera in the grammitids. Many of the genera consist of very few species and they are also hard to differentiate morphologically. I would much rather have just a few broadly circumscribed genera, which would also be helpful as a preliminary step in the species identification process (rather than something you look up after having identified the species). The smaller clades could still be recognised as subgenera, which would allow communicating the same phylogenetic information but would simplify the nomenclature considerably.

[msundue]

Htuom, I also pushed back against this classification within our grammitid working group for similar reasons. We considered other alternatives, but found this to be a balance of diagnosability, geography, and precedent. I am now in favor of these current genera.

Like many groups, the grammitids pose some challenges when we try to adhere to monophyly. In some cases, you will see that we have in fact sunk morphologically distinctive groups into larger genera in which they are nested in order to minimize genera (e.g. Zygophlebia into Enterosora and Themelium into Oreogrammitis). In other cases, however, lumping did seem to simplify things to us. This has resulted in several small genera, but these aren’t likely to muddle your life -- many of them are geographically restricted and not represented in many herbaria. Lumping these into other genera, we think, would cause more confusion. My justification for each case is further explained in the original post.

[joelnitta]

This proposal was voted on during PPG Ballot 13 (voting period September 2024). A total of 69 votes were cast. There were 57 'Yes' votes (82.6%) and 12 'No' votes (17.4%). The proposal passes.