Circinaria arida

Circinaria arida (pebble ball lichen) is a .5-6 cm, light olive-brown custose lichen that grows on rock, often like a cluster of little light brown to olive balls growing on pebbles, in the southwestern deserts of North America.^[1][1] It is also found in Eurasia, and arid parts of North America from the southern Great Plains and Midwest to California.^[1][2] It is warty (verrucose)with the warts sometimes cracking apart areolate.^[2] The warts or areolas have angular to rounded sides.^[2] The 0.2-2.3 mm, convex to flat-topped areolas are separated by deep fissures that may be as deep (0.1-2 mm) as the areaola is wide, so the lichen often appears to be made of clusters of little balls crammed up next to each other, although the areolas are sometimes isolated.^[2] In California it is commonly found growing on pebbles.^[1] Each areola has a single sunken black, dust covered (pruinose) fruiting body (apothecium) with a white rim.^[1] A thin strip of prothallus sometimes is at the outer edge, forming a narrow dark zone (fimbriate).^[2] The similar Aspicilia desertorum has a white pruina (dusty coating) on the apothecia.^[2] It is negative for lichen spot tests, I-, K-, P-, C-.^[1]

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