Changes coming for Thelypteridaceae (ferns)

A large and long-awaited update to the taxonomy of the maiden fern family, Thelypteridaceae (currently Thelypteris, Parathelypteris, Christella, Cyclosorus, Pneumatopteris, etc.) has just been published by Susan Fawcett and Alan Smith. The family represents about 10% of extant fern diversity, and Susan and Alan have divided it into 37 genera, some new, and provided extensive descriptions of each and a key to genera. Their work was published in Sida 59: you can order a hard copy or a free PDF download https://shop.brit.org/books?page=1. See this short thread by Wes Testo https://twitter.com/westo_fernnerd/status/1447956178680565762 on why this is important for pteridology.

I feel pretty confident that this classification will be well-received, but it will entail a few changes to familiar taxa.

United States: the biggest change (in terms of observations impacted) is the transfer of New York Fern from Parathelypteris to an enlarged Amauropelta. Nevada fern goes with it; Massachusetts fern to Coryphopteris while marsh fern is unaffected. In the south, many, though not all of the large ferns treated in Thelypteris, which have been listed under Christella in Weakley’s Flora, will go to a new genus, Pelazoneuron. This will allow some more specific genus-level IDs for taxa like T. kunthii vs. T. ovata, often hard to distinguish in iNat photos.

New Zealand: relatively few thelypterids are found here, but gully fern will go from Pneumatopteris pennigera to Pakau pennigera as the former genus turned out to be a number of marginally related groups bundled together.

Several of the common tropical species will not change their names under this classification, particularly Christella dentata, C. hispidula, C. parasitica, Cyclosorus interruptus, and Macrothelypteris torresiana. In theory, impacts should be bigger in the tropics where most of the group’s diversity lies, but in practice, people rarely dare identify that diversity to species. I am hopeful that the new classification will make it easier to do at least genus-level IDs on many thelypterids.

This will take some time to roll out, and I think some of the swaps will run up against the load limits and require scheduling by staff. I think this is a good set of changes, and will improve our understanding of the family, but I wanted to put this out here to attract feedback and avoid surprises.

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i vote we skip it and wait ten minutes for the next six revisions of fern taxonomy to come out. in fact i’d step new york fern back to Thelypteris.

I fully expect to be overridden here, i realize that. But especially for ferns, trying to untangle genetic phylogeny is pretty hopeless as they are backcrossed hybridized multiple ploidy levels etc etc etc. There aren’t ever going to be clear cut species and family trees so we need to just choose something that is simple and elegant and functional.

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Although I haven’t studied this particular group before yet, generally it may be best to wait at least some time to confirm that it is well-received in literature, and/or contact authors of this revision and other authors in the field to learn what they think. Not that the changes “can’t” be made now, but something to at least consider, and also to check other curators’ views on this first.

Will Macrothelypteris be affected?

Not really. Circumscription of the phegopterid genera (Macrothelypteris, Phegopteris and Pseudophegopteris) is essentially unchanged; one African species has been transferred from Macrothelypteris to Pseudophegopteris (P. rammelooi).

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