Collema is a genus of lichens in the family Collemataceae. The photobiont is the cyanobacterium genus Nostoc. Species in this genus typically grow on nutrient-rich bark or somewhat siliceous or calcar

Collema nigrescens is a leafy jelly lichen found growing on the bark of trees such as bigleaf maples, in wetter coastal parts of California. It is commonly called button jelly lichen or bat's wing lic