About Phlyctis argena (Ach.) Flot.
Phlyctis argena (Ach.) Flot. has a thin, crustose thallus that ranges in colour from white and greyish to green-grey. Identification can be confirmed with a potassium hydroxide spot test (K-test): applying a drop of potassium hydroxide to the thallus will make it turn yellow first, then red. This species is widespread, with a range that includes Africa, Asia, Europe, and North America. Phlyctis argena most commonly grows as a generalist epiphyte on the bark of deciduous trees, particularly Salix cinerea and Fraxinus excelsior. It occasionally also grows on stone, such as gravestones. This lichen is an acidophilic generalist epiphyte of deciduous trees. Its overall abundance has generally increased since the 1970s, which may be a response to changes in air pollution levels.
