Map lichen, twin map • Rhizocarpon geminatum

Photo by Jennifer Walker

This crustose lichen has the appearance of an oddly-coloured cracked patch of mud, or gravel embedded in tar: it is composed of small rounded, flat to convex, grey to grey-brown "discs" (areoles) surrounded by black (prothallus). It grows on well-lit acidic rock, and has a circumpolar distribution that in North America stretches from the Arctic to Maine, Colorado, Arizona, and California. Click here for more identification details.

iNaturalist
​https://www.inaturalist.org/taxa/229953-Rhizocarpon-geminatum

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References
NatureServe. (2015). Rhizocarpon geminatum - Korber Twin Map Lichen. NatureServe Explorer: An online encyclopedia of life. Accessed 09/02/2016.
Rhizocarpon geminatum Korber. Consortium of North American Lichen Herbaria. 

Authors and editors
Kelly Fretwell (2016).