Nothing else in the Sonoran Flora really works: P. ponojensis and P. rufescens are very different, P. praetextata shouldn’t have such richly tomentose/fibrillose rhizines, P. monticola is a very small species. This is very tomentose throughout the upper surface, which would be unusual for P. membranacea. Also, the veins are darker and less sharply defined than is typical for P. membranacea. Lastly, the rhizines of P. membranacea, while covered with minute “soft” erect hairs, are nevertheless clearly simple and nonfibrillose, at least near the margins. This thing has crazy brushy-fibrillose-tomentose rhizines. I’ve never seen a photo of P. fibrilloides. And Vitikainen describes it as having upturned margins. But otherwise it matches well enough. It doesn’t say much about habitat preference.