... now this is a delicate case, because there seems to be a very strong case by the European taxonomists to move undulata, its holarctic sister species, from Rheumaptera to Hydria. Hausmann & Viidalepp 2012 very clearly document the case for undulata in their publication. See also Stadie, Fiebig & Rajaei, Zootaxa 5092 (5): 501-530 (2022)

Here is the answer by Axel Hausmann on my question:

"Our European undulata was placed in Hydria after morphological analysis (Hausmann & Viidalepp 2012).

prunivorata was also in Hydria (e.g. Hodges 1983), then somehow ended up in Rheumaptera (Scoble 1999), the North Americans now seem to prefer to see both species in Rheumaptera (e.g. in BOLD), the closer relationship with undulata (which is also found in North America widespread) is also genetically based (p-distance: 3.56%). However, I am not aware of any taxonomic analysis in which North American experts have revised the assignment in Hausmann & Viidalepp (2012) and placed both species in Rheumaptera with justification. This is one of the many cases in which a transatlantic publication would have to contribute to the clarification. Who has the time for that? But it's true, it's stupid if one species is in Hydria and the other in Rheumaptera in the catalogue. Unfortunately, I don't see a satisfactory solution at the moment (unless we simply put prunivorata in Hydria in the catalog with a small note on genetic relationship...?" (Google translated)

To avoid problems with the "complex undulata/prunivorata", which is a technical issue of iNaturalist and doesn't work if the 2 species are in different genera, I would strongly suggest to have both in the same genus. Therefore I am doing this change now. If you wanted to discuss it, please contact the autors of the 2012 Hausmann & Viidalepp paper. Thank you.