Rhizoplaca chrysoleuca

Rhizoplaca chrysoleuca (orange rim lichen,^[2] rock-posy lichen, rockbright) is a pale yellowish-green to gray-green umbilicate foiliose lichen in the Lecanoraceae (rim lichen) family.^[3][4] It was first described in 1791 by English botanist Sir James Edward Smith as Lichen chrysoleucus; Friedrich Wilhelm Zopf transferred it to the genus Rhizoplaca in 1905.

The single-leaf (monophyllous) umbilicate thallus can be 2–3.5 cm in width, with deep lobes.^[4] The thallus is relatively thick and lumpy with warts and lobules.^[3] The fruiting structures (apothecia have lightly pruinose, burnt-orange to tan discs rimmed, with a contrasting rim of pale greenish thallus-like tissue making them easy to identify.^[3] Apothecia are 0.8–2.5 mm diameter, and often numerous and crowded into each other.^[4]

It grows in Eurasia and western North America. In the Sonoran Desert region it grows at elevations from 1,200 to 3,200 metres (3,900 to 10,500 ft).^[4] It prefers siliceous rock, granite, schist, quartz, mica, and basalt, but is also found on sandstone and less commonly on calcareous rock.^[4] It grows from the high desert to the alpine zone.^[4] It is often nitrophilous,^[4] preferring dropping areas under bird perches. It is common on rock in inland arid mountain and desert habitats in California.^[3]: 118

Lichen spot tests are K+ yellow or K−, KC+ yellow-orange, C−, and P− on the cortex, and K−, KC+ red or KC−, C−, and P+ yellow or P− on the medulla.^[3]