It only rarely has apothecia, instead reproducing most often vegetatively via soredia, which are piled in round blue-gray mounds across the thallus's upper surface.

It grows on both dry stone and that moistened by seepage, and can survive being irregularly submerged for extended periods underwater.

Physcia caesia was first described by German botanist Georg Franz Hoffmann in 1784 as Lichen caesius.

[5] The nomenclatural database MycoBank considers the taxon Physcia wainioi, one of its many synonyms, to be a distinct species.

[6] The genus name Physcia means "inflated" or "sausage-like", referring to the form of the type species.

[9] It has blue-gray soredia, which are piled in round mounds (such aggregations are known as soralia) across the thallus's upper surface.

[9] Where present, these are black discs measuring up to 2 millimetres (0.08 in) across, with prominent thalline margins (which means the thallus extends up around the edges of the apothecia) and a grayish pruinescence.

[3] Physcia caesia is widespread across much of the world, found in Arctic, boreal and temperate vegetation zones.

[11] Though found across much of North America, it is absent from central and southeastern United States, parts of the Great Basin, and northern Alaska.

[9] In South America, it is found in Argentina, Chile, and Peru; common and widespread in temperate areas, it occurs only rarely and only at elevations above 3,700 m (12,100 ft) in tropical regions.

[16] It is described as "cosmopolitan" in New Zealand,[14] has been reported from a number of sites in southeastern Australia and Tasmania,[17] and also occurs in Antarctica.

[9] It is uncommon on bark;[9] however, in the Colorado Rocky Mountains, it is one of the predominant lichens on juniper trees, growing primarily within 0.1 m (3.9 in) of the ground on the northern and eastern side of trunks.

[10] Physcia caesia tolerates a variety of locations, occurring on vertical, angled and horizontal surfaces, as well as rocky overhangs.

[27] Physcia caesia is known to accumulate high concentrations of heavy metals, including chromium, zinc, copper and iron.

[3] In Poland, it is part of bryophyte communities found on asbestos tile roofs, occurring with Tortula ruralis, Orthotrichum anomalum, Grimmia pulvinata, Schistidium apocarpum and others.

[32] As with most lichens, Physcia caesia is impacted by habitat loss through development, as well as by the trampling or overgrowth of its location.