Acarospora socialis

Acarospora socialis (bright cobblestone lichen) is a usually bright yellow areolate to squamulose crustose lichen in the family Acarosporaceae that grows up to 10 cm wide, mostly on rock in western North America.[1] It is among the most common lichens in the deserts of Arizona and southern California.[2][3]^: 218–9[3]^{: 218–219} It grows on sandstone, intrusive and extrusive igneous rock such as granitics, in all kinds of exposures to sunlight, including vertical rock walls.[1] It is found in North America, including areas of the Mojave Desert and Sonoran Desert region, to Baja California Sur.[1] It is the most common yellow member of its genus in southwestern North America.[1] It sometimes, but rarely, grows on other soil crusts.[1] It is a pioneer species.[1]

Acarospora socialis
Scientific classification
Domain:	Eukaryota
Kingdom:	Fungi
Division:	Ascomycota
Class:	Lecanoromycetes
Order:	Acarosporales
Family:	Acarosporaceae
Genus:	Acarospora
Species:	A. socialis
Binomial name
Acarospora socialis H.Magn. (1929)

Close-up view

It is variable in its growth pattern.[1] Areoles can be angular to round, sometimes forming lobes. They can be contiguous or scattered.[1] Color is variable - bleached white, green-yellow, and other hades of yellow.[1] It has a lower surface when squamulose, but without a lower cortex.[1] With age, it forms stipes.[1] Each squamule has 0 or one 1 mm round to angular apothecia immersed in it, outside desert habitats, but may have 2 to 10 per in deserts.[1] Two apothecia may merged leaving a peninsula (umbo) of thalline tissue through the disc.[1] Apothecia may have lecanorine margins.[1] Apothecia have a flat to concave mostly brown or reddish brown, concave disc.[1]

Lichen spot tests are all negative.[1] It is UV+ orange.[1] Secondary metabolites include rhizocarpic acid, and sometimes trace amounts of epanorin.[1]

When young, it is very similar to Acarospora contigua.[1] But A. socialis has areolas that become lobed and squamulose.[1] When appearing on soil, it may be mistaken for Acarospora schleicheri.[1] But A. socialis has contiguous areoles while those of A. schlecheri can be imbricate.[1] It is also similar to Acarospora chrysops, which grows from South America to central Mexico, through Texas and into the Rocky Mountains.[1] It is very similar to Pleopsidium flavum at mid-level mountains, with the latter favoring higher elevations, above 900 metres (3,000 ft), and being somewhat effigurate with smaller (less than 1 mm) yellow apothecia.[1]