Unfortunately it’s been a bit since my last post, but fortunately some of that time was spent staring intently at rocks, trees and dirt on the west slope of Colorado. Since I had not spent much time at all in that part of the state after my infatuation with lichens began, I did not know what to expect. What I certainly did not expect was for Rhizoplaca novomexicana to be by far the most conspicuous lichen in my travels.

Called New Mexico Rim-Lichen by some authors, there are specimen records for most of the mountain west from the Mexico border just reaching Canada. In Colorado, it can be found just about anywhere including the plains and the high tundra, rocks required. Along the Front Range it is rather local on sunny rocks and more common above timberline. But judging from four days spent near the Utah border it can be found anywhere out west, I found some just about anywhere I looked, especially on sandstone. As a taxonomic note this species was long in the huge Lecanora genus, that is before modern taxonomists carved it up into a dozen or so new genera. Within the genus Rhizoplaca it stands out by being truly crustose. It’s close relative Rhizoplaca chrysoleuca is attached at single point, like a very short tree trunk, or umbilicate in lichen terms.

In identifying this species, narrow down your search criteria first by a high level description. It’s crustose, it has lobate margins, and it has plenty of apothecia. This lichen can be sterile but usually a fertile specimen is nearby. Next up note the rather unique yellow-green color of the overall thallus. Also a nice clue, is that this species is often missing older parts of the center of the thallus as in the lichen to the right.

The key I first used to identify this species, Brodo’s Lichens of North America, makes a big point of the shape of the margins. They are distinctly raised vs flat and instead of overlapping form tiny winding canyons. This is also a important characteristic of the most common lobate crust along the front range, Protoparmeliopsis garovaglii. To close out the ID check out the color of the apothecia. They should nearly black to a kind of bluish grey; there always seems to be a hint of cobalt color if you look carefully enough. Often, but not always, the apothecia are dusted in a yellow pruina like the individual below.

I am excited to share some of the other tales from exploring the dusty canyons of western Colorado. So hopefully a quick introduction to a new fungus whetted your appetite.