Cracked Shield

Parmelia sulcata is a common lichen usually found in northern areas, but samples have often been found down the California coast.  Cracked Shield has flat gray green leaf like structures with network of cracks and ridges and is not as sensitive as other lichen species to pollutants.

Lichens grow in the leftover spots of the natural world that are too harsh or limited for most other organisms. They are pioneers on bare rock, desert sand, cleared soil , dead wood, animal bones, rusty metal, and living bark. Able to shut down metabolically during periods of unfavorable conditions, they can survive extremes of heat, cold, and drought.

Lichens are composite, symbiotic organisms made up from members of as many as three kingdoms.

The dominant partner is a fungus. Fungi are incapable of making their own food. They usually provide for themselves as parasites or decomposers.

"Lichens are fungi that have discovered agriculture" -- lichenologist Trevor Goward.

The lichen fungi (kingdom Fungi) cultivate partners that manufacture food by photosynthesis. Sometimes the partners are algae (kingdom Protista), other times cyanobacteria (kingdom Monera), formerly called blue-green algae. Some enterprising fungi exploit both at once.

http://www.lichen.com/biology.html

The type of algea that Parmelia sulcata incorporates is called Trebouxia.

http://www-biol.paisley.ac.uk/bioref/Chlorophyta/Trebouxia.html