Diorygma nigricans

This species is a bark-dwelling crustose lichen with a light green-gray thallus that can reach about 5 cm (2 in) across and is 80–150 μm thick. The surface is uneven and lacks a cortex, and parts of the thallus may flake away. The photosynthetic partner (photobiont) is from the green algal genus Trentepohlia (cells 8–12 × 6–8 μm). The medulla is white and contains many clusters of calcium oxalate crystals, and the base includes a strongly carbonized (blackened) layer about 30–70 μm thick.^[2]

The fruiting bodies are lirellae that are flexuose, densely branched, and often arranged in star-like clusters. They are immersed, 0.5–3 mm long and 0.2–0.4 mm wide, with a thick white thalline margin. The exposed disc is brown-black and lacks pruina. Ascospores are single per ascus, ellipsoid, richly muriform, and measure 80–120 × 20–30 μm; they are colorless and iodine-positive (I+ violet-blue). Reported secondary metabolites include lichexanthone (UV+ yellow) and stictic and constictic acids as major substances, with cryptostictic, hypostictic, and hypoconstictic acids in smaller amounts.^[2]

The species is known from Amazonian Peru (Madre de Dios), where it was collected at about 270 m (890 ft) elevation in tropical lowland rainforest, growing on tree bark in secondary forest.^[2]