''Collema nigrescens'' is a leafy ( foliose) jelly
lichen
A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.Collema genus) found growing on the bark of trees such as bigleaf maples, in wetter coastal parts of California.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, It is commonly called button jelly lichen or bat's wing lichen. It is blackish-green when wet, and dark brownish-green to dark olive when dry. The photosynthetic partner is the ''
Nostoc
''Nostoc'', also known as star jelly, troll’s butter, spit of moon, fallen star, witch's butter (not to be confused with the fungi commonly known as witches' butter), and witch’s jelly, is the most common genus of cyanobacteria found in vari ...
'' cyanobacterium that is spread throughout the thallus (main body part). Although foliose in form, like all jelly lichens, the thallus is not differentiated, lacking layers or an upper or lower cortex (lichen) and the cyanobacteria is spread throughout the thallus. It has dark purple-brown apothecia all over. It produces no reaction to lichen spot tests.