Phlyctis argena
# 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
