Circinaria rogeri

The thallus is somewhat fruticose and forms unattached, shrubby clumps that are typically 0.5–2 cm (0.2–0.8 in) across. Branching is usually irregular (only rarely neatly forked), and the tips are often pale with a small blackened area where pycnidia are common. The surface is generally dull yellow-green to olive-green or olive-brown, sometimes gray-green, and pale pseudocyphellae (small, pale breaks in the surface) are usually most obvious toward the branch tips. In cross-section, the cortex (outer "skin") is distinctly two-layered, with a thin outer layer of rounded cells and a thicker inner layer of elongated cells. Apothecia are uncommon. When present they are dark, often pruinose, and may become adnate to short-stalked, reaching about 2.5 mm in diameter. The ascospores are hyaline and simple, while the conidia are threadlike and typically about 7–16 μm long. No secondary metabolites were detected, and standard chemical spot tests are negative (K−, C−, KC−, P−).

Aspicilia rogeri is an obligatory vagrant on calcareous soils in open shrub-steppe. It favors sites that are briefly moist in winter or spring but dry for most of the year, and it has often been recorded at elevations of about 1,000–2,000 m (3,300–6,600 ft). It is associated with calcareous badlands landscapes, including habitats dominated by black sagebrush (Artemisia nova) and other Artemisia communities, and it may occur alongside other soil-crust lichens such as Aspicilia hispida. The species is known from western North America, with published records from Colorado, Idaho, Oregon, Utah, and Wyoming. In their global review of manna lichens and relatives, Sohrabi and coauthors treated it as restricted to North America (in contrast to several related vagrant species that are widespread in Eurasia).

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