Moriarty and Cannatella (2004) write:

"The phylogenetic analyses of Cocroft (1994) and Da Silva (1997) are consistent with Hedges (1986) transferral of crucifer, regilla, cadaverina, and ocularis to a monophyletic Pseudacris. Our tree provides strong support for the monophyly of the genus including these taxa. Given that most checklists and field guides (Stebbins, 1985, is an exception) follow Hedges' taxonomy,
we continue it here."

Moriarty and Cannatella give no compelling reason for classifying crucifer, regilla, cadaverina and ocularis in Pseudacris. Morphologically most of these species are more like Hyla than Pseudacris in having well developed toe pads. Hyla cadaverina is an excellent climber. Even though Hyla regilla is more likely to be found on the ground than in trees in the wild, it too is an excellent climber. The genus Pseudacris, on the other hand, is an assemblage of secondarily terrestrial species with reduced toe pads. Immunological data also suggests that Hyla regilla, Hyla cadaverina and Hyla crucifer are basal to Pseudacris. Hyla crucifer is the species closest to Pseudacris phylogenetically. Hyla regilla and H. cadaverina both lie outside of the Pseudacris-H. crucifer clade. Therefore it is certainly possible to leave Hyla regilla and Hyla cadaverina outside of Pseudacris even if one were to insist on a holophyletic Pseudacris. Moriarty and Cannatella's decision to "follow most checklists and field guides" is a weak reason for maintaining a morphologically heterogeneous Pseudacris.

Stebbins' (1985) placement of regilla and cadaverina in Hyla is therefore justified on morphological grounds. "Most checklists" and field guides often blindly follow the latest taxonomic proposals. It appears that Stebbins has evaluated Hedges' taxonomic proposal and rejected it. I do not always agree with Stebbins' taxonomic decisions, but it appears that he does evaluate taxonomic proposals and in this case I think he has made the correct one in retaining these species in Hyla in the latest edition of his field guide. Further, immunological data by Maxson shows that Hyla cinerea, Hyla arborea and Hyla regilla form an unresolved polytomy. That means if Hyla regilla is included in Pseudacris, both Hyla arborea and Hyla cinerea may need to be included in Pseudacris as well, if one is using Moriarty and Cannatella's own Hennigian classificatory philosophy, which states that a taxon must include one ancestor and all of its descendants. However, if Hyla arborea is included in Pseudacris, it makes Pseudacris an invalid name, since Hyla arborea is the type species of Hyla and since Hyla is the earlier name, it has priority over Pseudacris under the rules of the ICZN. Moriarty and Cannatella have apparently ignored Maxson's immunological data but since their analysis does not include H. arborea, they cannot exclude the possibility that Hyla arborea and Hyla cinerea form a clade with Pseudacris, H. regilla, H. cadaverina and H. cinerea.

In sum, by including H. regilla and H. cadaverina in Pseudacris, Moriarty and Cannatella have not only created a morphologically heterogeneous group, with most members having reduced toe pads and a few having well developed toe pads, but they may have also created a potential can of taxonomic worms.

Reference

Moriarty, Emily C. and David. C. Cannatella 2004. Phylogenetic relationships of the North American chorus frogs (Pseudacris: Hylidae). Molecular Phylogenetics & Evolution. 30(2):409-420

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