About Physcia stellaris (L.) Nyl.
Physcia stellaris (L.) Nyl. is a foliose leaf-like lichen. Its thallus is irregular in size and shape, and can grow up to 4 cm in diameter. Its lobes are loosely appressed, with an average width of just 0.5 mm. The upper surface of the thallus is whitish-grey, nearly cream in color, and lacks any soredia or isidia. The lower surface ranges from white to brown, and bears simple rhizines. Abundant apothecia grow to between 0.5 mm and 1.5 mm across; these are lecanorine, meaning the fruiting bodies are plate-shaped and surrounded by a ring. Each ascocarp contains 8 brown, septate ascospores that measure 15 to 18 μm in size. P. stellaris can be distinguished from almost all other Physcia species by its complete lack of soredia; the only exception is Physcia aipolia. P. aipolia differs from P. stellaris by having broader lobes and typically pruinose apothecia. This species is commonly found growing as a lichen on bark and rock throughout temperate zones of North America and parts of Europe. Documented occurrences of the species in North America range from Georgia to the Canadian Northwest Territories. It is quite common on deciduous trees, and occurs less commonly on conifers. Because P. stellaris lacks isidia and soredia, it shows no visible form of asexual reproduction. It produces abundant apothecia for sexual reproduction.
