Aspicilia cinerea (aka “Cinder Lichen”)
Description: Thallus thin or thick, continuous & rimoseareolate to somewhat verrucose, very pale to rather dark greenish gray or ashy gray (in some populations, yellowish gray or chalky white). Apothecia black, mostly 0.4-1.2 mm in diameter, disk level with the thallus surface & marginless or with a thin, slightly prominent margin often darker than the surrounding thallus; spores 12-22 x 6-13 um, 4-8 per ascus; conidia 11-18(-22) x 1 um.
Chemistry: Medulla PD+ yellow, K+ red, KC-, C- (norstictic acid), or PD+ orange, K+ persistent yellow (stictic acid).
Substrate: On siliceous rocks usually in sun, often covering very large surfaces.
Lookalikes: In North America, several species that contain norstictic acid but differ in thallus color & development as well as substrate type can be found in museums filed under “A. cinerea.” We accept populations with stictic acid & thin, rather smooth to rimose thalli as a variety of A. cinerea if all other characters agree. Aspicilia verrucigera has a rather thick thallus that usually builds into curved & lumpy, somtimes worm-like areoles & contains stictic acid; it is one of the most common species of the genus, especially in eastern North America. Aspicilia cinerea generally has a thinner, less bumpy thallus. Like A. cinerea, A. verrucigera grows on granitic rocks in full sun, & the two species often grow as neighbors. Specimens that are similar to A. cinerea but lack lichen substances & have a blues gray, rimose-areolate thallus are often called A. caesiocinerea. Specimens with a K+ medulla, but growing on limestone, are common in the west. They usually have creamy white thalli & probably represent other species.
Bibliography: Lichens of North America, by Brodo, Sharnoff, & Sharnoff
Database Entry: Distance Everheart 12-26-13