Phlyctis argena

Phlyctis argena is a species of crustose lichen.

Description
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.

Range
Widespread, including Africa, Asia, Europa and North America.

Habitat
Phlyctis argena usually grows as a generalist epiphyte on the bark of deciduous trees, especially Salix cinerea and Fraxinus excelsior. It also occasionally grows on stone, such as gravestones.

Ecology
The lichen is a generalist epiphyte of deciduous trees and is acidophilic. Its abundance appears to have increased generally since the 1970s, possibly in responses to changes in pollution levels

Etymology
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.

Taxonomy
The following varieties of Phlyctis argena have been described:
 * Phlyctis argena var. argena
 * Phlyctis argena var. gilvoalbicans
 * Phlyctis argena var. erythrosora
 * Phlyctis argena var. nubilosa