title: Phlyctis argena
text: # 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
  