Phlyctis argena (Spreng.) Flot.

Phlyctis argena is a conspicuous lichen; its whitish to pale grey thalli, circular at the beginning, attract attention even from distance. The thalli are covered with coarse soredia and surrounded by a white prothallus. They contain norstictic acid, which gives at first a yellow, gradually turning blood red KOH reaction. However, the reaction is weak when the acid concentration is low. Apothecia are rare, resemble soralia, and there is a single gigantic muriform spore in an ascus.

Phlyctis argena is an abundant lichen of deciduous trees. It is often one of the first colonizers of smooth bark. It is rarely found also on wood and basic silicates. The species occurs across Europe in forests and open countryside. In the Czech Republic it is common from lowlands to mountains.

Ascomycota → Lecanoromycetes → Ostropales → Phlyctidaceae → Phlyctis