Description: Thallus leprose, cottony, whitish to greenish grey, often with a yellowish tinge, sharply delimited, orbicular at least when young, usually without marginal lobes, but sometimes almost sublobate, consisting of a mass of powdery, spherical, up to 200 µm wide granules with up to c. 40 µm long, protruding, but never clam-shaped hyphae. Medulla white, not always evident, UV+ violet, the hyphae 2-5 µm thick, covered in small colourless crystals. Photobiont chlorococcoid, the cells up to 20 µm diam. Spot tests: K- or K+ yellowish, C+ faintly yellow or pink, KC+ pink to reddish orange (reaction sometimes ephemeral), P+ yellow slowly turning orange or P+ rapidly orange, UV-. Chemistry: three chemotypes: 1) alectorialic acid only, 2) alectorialic and protocetraric acids, 3) alectorialic and psoromic acids.
Note: on a wide variety of substrata, mostly on old trunks with subneutral bark, but also on rocks (including walls in urban areas), soil and mosses, avoiding very acid substrata and mostly on more or less rain-sheltered surfaces; certainly more common throughout the country, below the subalpine belt.
Growth form: Leprose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)