Parmelia sulcata is everywhere! You can find it from sea level thickets to high in the mountains, on high desert sagebrush and seasonally flooded Oregon ash. It may reach its densest concentrations in urban environments, because in thrives in areas with high atmospheric nitrogen, and is tolerant of many other forms of pollution.
Back in my callow youth I assumed these Parmelia lichens were either shredded or deformed bark. They are not starkly ‘other’ from the tree the way that Evernia and Ramalina are, and require a closer look to perceive independence. Parmelia as a genus are relatively easy to identify, because of the grayish dorsal and black ventral surfaces. But a hand lens, or possibly just very good ability to close focus ones eyes, is required to spot the shapes of the rhizines which are diagnostic to each species. To further complicate things there are chemotypes of P. sulcata, which some feel are separate species. More on that here.
Description– Loosely appressed, foliose thallus, light grey to greyish green; lobes 1-4mm, with lighter angular lines; soredia on margins and along angular cracks; lacking isidia and apothecia rare; rhizines squarrose (branching at right angles) in the field, though mostly simple at the edges.
Similar species– Nothing else has the combination of angular cracks with powdery soredia, and squarrose rhizines.
Habitat-Usually found on bark or wood; occasionally on rock or mossy rock.
Range-Cosmopolitan; found throughout our region.
Eaten by– Hummingbirds like to use this lichen to line their nests; Many cultures have made a brownish yellow dye from its extracts.
Etymology of names–Parmelia is Greek for ‘small shield’, alluding to the tendency of some members of this genus to form roughly circular groups of thalli. The specific epithet sulcata means ‘with furrows’, but I can’t ascertain which furrows this references.