Lepra amara (= Pertusaria amara) is a light grey crustacean lichen that is often well seen on the blackish bark of evergreen oak trunks. The thallus of Lepra amara can reach 20 x 30 cm, although the boundaries between specimens may not be clear. In this thallus, the soralia, made up of granules containing soredia, stand out as a roughly convex circle of 0.5-2.0 mm in diameter. Soredia are ready for dissemination packs of enveloped in fungal hyphae algal cells. Lepra amara almost never produces apothecia for sexual reproduction, it relies on the dispersion of its soredia to multiplicate.
Lepra amara differentiates from nearby species by its positive KC (potassium hydroxide + sodium hypochlorite) reaction of an intense red wine colour, and by its bitter taste that results from the picrolichenic acid content.
Lepra amara is a common and widely distributed species of lichen. In addition to the bark of evergreen oaks, Lepra amara may also grow on the bark of other trees such as cork oaks, oaks, maples, or lime trees, and on siliceous rocks.
[photo Jordi Badia, identification by Maria José Chesa]