Description: Thallus bright sulphur-yellow to greenish yellow, composed of scattered or contiguous areoles 1-2.5 mm in diameter, convex or flat, with smooth or scalloped margins, sometimes lightly dusted with a white pruina. Apothecia reddish brown to very dark brown, immersed in the areoles, 1-4 per areole, sometimes becoming somewhat prominent with thallus-colored margins; disks often broken up with patches or a network of sterile thallus-colored tissue; spores ca. 3-4 x 2-3 um, many per ascus.
Chemistry: Cortex & medulla PD-, K-, KC-, C- (pulvinic acid pigments).
Substrate: On siliceous rock in open, arid sites.
Range: Probably widespread throughout the arid southwest, but also known from glades in the Ozarks.
Lookalikes: The closely related A. schleicheri grows on soil & has a more marginally lobed thallus. The taxonomy of this group is still poorly worked out, & so precise distribution maps of A. contigua & A. schleicheri are impossible at this time.
Bibliography: Lichens of North America, by Brodo, Sharnoff, & Sharnoff
Database Entry: Distance Everheart 12-26-13