That's curious. I suspect that POWO is out of date given its acceptance of C. austromontana Standl. & Blumer. C. nelsonii Eastwood has priority by a couple of years (here). I can't speak to C. aspera; POWO lists it as from northern Mexico only, and it's not listed in the index of the just-released FNA vol. 17 (FNA excludes Mexico). @markegger is an author of the section on Castilleja in that volume and I'm sure can address this in more detail.

To clear things up, after my studies of Mexican Castilleja species over two decades, it became clear that the se AZ and sw NM species, long known as C. austromontana in local floras, was actually synonymous with the earlier described but little known entity, C. nelsonii, described by Eastwood in her monograph on the paintbrushes of Mexico in 1909. The type of C. nelsonii is from Cerro Mohinora in far sw Chihuahua. The situation with C. aspera is a little more complicated. In the same paper where she described C. nelsonii, she also described C. nervata and C. aspera. C. nervata is a "good" species, but C. aspera is problematic. The type collection consists of three sheets. Of the multiple stems present, all but one are clearly referable to C. nervata, while the final one is a specimen of nelsonii/austromontana. The designated holotype sheet at GH contains a stem of C. nervata and the single stem of C. nelsonii, so lectotypification is required. None of the C. aspera collections were from the US, so dealing with it in the FNA was not appropriate. I hope to publish a synopsis of Mexican Castillejas in coming years, where I will first lectotypify C. aspera and then place it into synonymy under one of the two accepted species. In the FNA treatment, which will hopefully be indexed into POWO soon, C. nelsonii is the accepted name, with the later C. austromontana listed as a synonym thereof. C. aspera, as I mentioned, is not addressed in the FNA, but I would strongly advise not accepting it on iNat, due to the major problems in both its typification and because it will eventually become a published synonym. Hope this all makes sense!