Lecanora viridipruinosa

Lecanora viridipruinosa forms a patchwork of separate, flat-topped areoles—tiny crust pieces 0.5–1.5 mm across—that sit tightly on the bark or rock. Each areole is dull white but may be ringed by a soot-black fringe of cyanobacteria. There is no visible mat (hypothallus) beneath the crust. Inside, the lichen's photosynthetic partner (photobiont is a single-celled green alga whose round cells are 8–15 μm in diameter.^[1]

The fruiting bodies (apothecia) appear one by one on the areoles. They begin half-buried but soon stand clear, 0.5–0.8 mm wide, with a smooth black disc and a matching, very thin rim. As they mature the discs swell into low domes and usually pick up a faint green frost (pruina); a drop of potassium hydroxide solution dissolves this green film. A microscopic section shows a 45–70 μm tall, clear hymenium topped by a green-tinged epihymenium. Slender, branching paraphyses thread this layer; their tips carry a cap of the same green pigment. Below lies a pale to orange-brown hypothecium that may trap the occasional algal cell. Each ascus is broadly club-shaped (clavate) and holds eight smooth, colorless ascospores. The spores are thick-walled, broadly ellipsoid, and measure about 10 × 5 μm, with no internal cross walls (septa).^[1]

No asexual reproductive structures are known. Standard spot tests give C−, K+ (yellow) on the thallus and HNO₃+ (red) on apothecial sections. Thin-layer chromatography detects the common lichen products atranorin and zeorin, but no other secondary metabolites. These features—white crust, green-dusted black apothecia, and thick-walled single-celled spores—make L. viridipruinosa recognizable among the many small, dark-disc Lecanora species.^[1]

• List of Lecanora species