World distribution: Physconia grisea is known from Europe, North America, Nepal, Australia, and New Zealand (Coppins 1992c). It is common in Central and South Europe. In Scandinavia it is a southern species, common only in Skåne and Denmark (Moberg 1977, Alstrup & Søchting 1989)
Ecology: Results. Locality 332 is a farm where the species occurred on 30 trunks of Ulmus glabra, 3 of Malus sp. and 2 of Acer pseudoplatanus; Punctelia subrudecta was also found at this site. Locality 2413 is within the city of Mandal, where intact populations with high abundance of the species was found on 20 scattered trees of Acer pseudoplatanus, Fraxinus excelsior, and Tilia sp.; here Melanelia laciniatula was also found. The species has not been recorded from rock in Norway. Discussion. In Norway, Physconia grisea seems to be confined to basic, usually dust-impregnated bark of tree trunks in urban and agricultural sites. Outside Scandinavia the species is also frequent on rocks, especially calcareous walls and memorials (Coppins 1992c). In Europe it is common even in moderately polluted areas (Barkman 1958, Hawksworth & Rose 1970). The species is moderately fertilizer-resistant (Brown 1992). Physconia grisea seems to prefer the south-facing side of trunks with rough bark, and is in the Netherlands particularly abundant on Ulmus along dusty roads where even the lichens themselves may be covered with dust (Barkman 1958). Physconia grisea normally grows together with several species of the genera Physcia, Phaeophyscia, Physconia, and Xanthoria (Barkman 1958, James et al. 1977). In the Netherlands it is often found together with Hyperphyscia adglutinata (Barkman 1958). The species is able to keep pace with epiphytic mosses (Barkman 1958)
Threats: Results. Recorded threats were land development and air pollution (1180). Discussion. The species probably benefits from agricultural dust. Too heavy loads of nutrients from agriculture and abandonment of farms may, however, negatively impact P. grisea. The Dutch elm disease represents a threat (cf. Watson et al. 1988), since Ulmus glabra is quantitatively the most important substrate in Norway (as well as in Bretagne, northwestern France, Belgium, and the Netherlands; Barkman 1958)
Status: Two old localities were visited. The species was abundant in one (332), and regarded as extinct on the other (331). One new locality was discovered, and altogether 55 trees are known to carry the lichen in the two sites. The species is obviously rare in Norway, although perhaps overlooked. Since it favours well-lit trees in man-made habitats, and is likely to be moderately resistant to SO2, it is probably not directly threatened
Specimens in other herbaria, litterature, etc.