Physconia perisidiosa (Erich.) Moberg
Thallus foliose, rosette-shaped, 2-5 cm diam., loosely appressed to the substratum, composed of lobes, intricate, radiating, short, 1-1.5 mm wide, pruinose towards margins, brown-greenish, pale brownish, pale greyish, occasionally tinged purple mainly towards the center, covered with dull white labriform soralia, mostly marginal, and with a few isidia, lower surface center dark brown, much paler towards the margins, margin devoid of cortex, brown rhizines, bottle-brush-shaped. Apothecia very rare, thalline exciple with sorediate lobules. Ascospores brown, thick walls, 1-septate, 26-35 x 16-21 µm. Chemical spot test negative, notably white medulla is K-. Rare species growing on nutrient-rich substrata on mossy trunks of ornmental trees aligned along roads or in parks sometimes on rocks and walls. See Physconia enteroxantha of which the yellow medulla is K+ yellow. See also Physconia grisea which has simple rhizines and Physconia detersa montane and boreal species with only marginal soralia and longer radiant lobes.