Physcia

Physcia is a genus of lichen-forming fungi in the family Physciaceae. The widely distributed genus contains about 80 species. The genus is cosmopolitan, and has been extensively studied in various regions in the past several decades, with significant biodiversity in South America identified as a central diversity hotspot. Physcia species are foliose, lichens that grow with a loose to close appressed habit. Their upper surface is typically whitish, pale greenish, green-grey, or dark grey in colour. The thallus colour remains relatively unchanged when moistened. Physcia lichens typically grow on bark, on wood, or rock, although they have occasionally been recorded dwelling on man-made structures. They thrive in nutrient-rich environments and are expanding rapidly in urban areas of the United Kingdom previously affected by SO2 pollution.

The main characteristics that separate Physcia from similar genera in the same order, including Dirinaria, Heterodermia, Hyperphyscia, Kashiwadia, Phaeophyscia, and Pyxine, are the distinct morphology of its (brown and two-celled), its somewhat cylindrical (asexual reproductive structures), and the presence of the chemical atranorin in the upper . Physcia has been divided into sections based on morphological and chemical , such as the presence or absence of on the thallus margins and K+ (yellow) spot test reaction in the cortex.