It is on granitic and siliceous blocks in semi-desert


Rhizoplaca subdiscrepans_GPS_947.JPG
Rhizoplaca subdiscrepans_GPS_947_.JPG
Rhizoplaca subdiscrepans_GPS_947_1.JPG

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Jason! Thank You very much!
By: Igor (Igor_Yevdokimov)
2018-02-12 00:47:56 CST (-0600)

Jason! Thank You very much!

By: Jason Hollinger (jason)
2018-02-11 23:52:26 CST (-0600)

Although, the first two photo has two thalli of R. chrysoleuca in the center (The paler ones with orange apothecia.)

This is a difficult group. Color is subtle but very useful. R. melanophthalma has a slightly darker, grayer/greener thallus, and greener/grayer apothecial; R. chrysoleuca has paler, whiter thallus, and distinct orange or pink coloration in the apothecia. R. subdiscrepans is generally closest to R. chrysoleuca in coloration, although sometimes somewhat intermediate between melanophthalma and chrysoleuca. But the thallus of R. subdiscrepans has a distinctive thallus that’s formed of many tiny, strongly convex areole-like units. Compare to the two R. chrysoleuca in your first photo which form large, clearly distinct ~foliose units. R. melanophthalma, on the other hand, has an extremely variable thallus, varying from the distinct, foliose thalli of R. chrysoleuca to colonial aggregations which can look a lot like members of the Lecanora muralis group. (Steve Leavitt has found that_R. chrysoleuca_ and R. melanophthalma both have better-developed thalli than R. subdiscrepans R. melanophthalma is probably a heterogeneous mixture of several semi-cryptic species.) Fortunately, none of the many forms of R. melanophthalma looks exactly like R. subdiscrepans or R. chrysoleuca.

Definitely, the way to really learn this group is to find mixed populations. When they grow together, they are usually easy to distinguish. Your first photo is a good example, I think.