Lepraria impossibilis

Lepraria impossibilis forms a powdery to membranous thallus (lichen body) with a clearly defined margin.^[3] Its colour ranges from greenish grey to grey-brown with an orange tinge.^[4] The thallus develops distinct lobes about 1 mm wide and long, with raised edges. It has a thin, white medulla (internal layer) and a grey hypothallus (attachment layer). The reproductive structures consist of abundant, medium-sized soredia measuring about 0.1 mm in diameter. Unlike some related species, it lacks projecting hyphae from the soredia. The species can be identified by its distinctive combination of secondary metabolites, including lecanoric acid and pannaric acid 6-methylester.^[3] Although morphologically indistinguishable from Lepraria cupressicola (then known as L. atrotomentosa), these species can be distinguished chemically; L. cupressicola lacks pannaric acid-6-methylester but contains zeorin and fatty acids.^[2] Another species, L. vouauxii, is similar both morphologically and chemically to L. impossibilis, but can be distinguished by the presence of lecanoric acid.^[4]

This lichen grows on tree bark, as well as on mosses found on both soil and rock surfaces. It has been recorded in forest areas and open habitats across South and Central America, including El Salvador^[3] and Costa Rica,^[5] and has also been reported from Iran.^[6] It typically occurs in both forested and open areas.^[3] In South America, where it occurs in Bolivia, Chile and Peru, it grows in high-elevation, open Andean vegetation.^[4]