About Pleopsidium oxytonum (Ach.) Rabenh.
Pleopsidium flavum, commonly called gold cobblestone lichen, is a crustose lichen with a distinctive bright lemon-yellow to chartreuse color. It grows at high elevations ranging from montane to alpine zones, on vertical or overhanging hard felsic rock such as granite, in western North America. Its thallus has a placodioid growth form, growing in a circular outwardly radiating pattern with 1-millimeter wide lobed edges. This species is the vivid lime-green lichen often photographed on granite boulders in Oklahoma’s Wichita Mountains Wildlife Refuge. According to Professor Wayne Armstrong of Mount Palomar College, this lichen grows only a few millimeters per century, making it the slowest growing of all known plants in the broad sense (sensu lato). It was formerly classified under the name Acarospora chlorophana. It belongs to the genus Pleopsidium in the family Acarosporaceae. It is similar to Acarospora schleicheri, a terricolous lichen that grows on soil and only rarely grows on rock, and to Pleopsidium chlorophanum, which favors dry arctic or alpine sandstone cliffs and boulders.
