File:Dermatocarpon spp. - Flickr - pellaea (1).jpg

Trader Trail, Orilla Verde Recreation Area, near Taos, New Mexico, 20110328

I'm no longer convinced of these D. reticulatum. I was basing my ID here on Heiđmarsson's species concept which emphasizes the "farinose" lower surface. However, I cannot find a good definition of exactly what he means by this. He talks about the farina as being a sort of thallinospore, presumably like the "soot" under many species of Umbilicaria. But the Umbilicaria thallinospores are sooty black and clearly visible under a microscope. The farina here is more a dusty white powder and I haven't been able to isolate it in section under a microscope. The two in the photo here are the only specimens I've ever seen with this white powder. Yet D. reticulatum is allegedly as common as D. miniatum. It makes me wonder if North American lichenologists are using the same concept as Heiđmarsson, and indeed whether the taxon Heiđmarsson calls "D. reticulatum" actually occurs in North America at all. I recently examined all the collections at NY, and they consistently called specimens that were black and rough underneath D. reticulatum. Admittedly the roughness can turn somewhat granular and will even rub off of old specimens in the herbarium. But can this really be what Heiđmarsson called "farina"??