[1] Phlyctis argena has a thin crustose thallus that is white, greyish or green-grey in colour.

The identification can be confirmed with the spot test application a drop of potassium hydroxide (K-test) to the thallus, which will turn yellow and then red.

Phlyctis argena usually grows as a generalist epiphyte on the bark of deciduous trees, especially Salix cinerea and Fraxinus excelsior.

Its abundance appears to have increased generally since the 1970s, possibly in responses to changes in air pollution levels[2] The etymology of the genus name, Phlyctis, comes from the obsolete medical term phlyctidium, meaning a large blister.

The species epithet, argena, is derived from the latin "argentum", meaning silver.