Diorygma nigricans is a species of bark-dwelling, crustose lichen-forming fungus in the family Graphidaceae. It is a light green-gray lichen with distinctive wavy, densely branched, star-like fruiting bodies, known only from lowland tropical rainforest in Madre de Dios, Peru. The species was described in 2012 and is characterised by its large ascospores, each produced singly within the ascus.
Diorygma nigricans was described as a new species by Eimy Rivas Plata and Robert Lücking in 2012, based on material collected at Los Amigos Research and Training Center (CICRA) in Madre de Dios, Peru.
This species is a bark-dwelling crustose lichen with a light green-gray thallus that can reach about across and is 80âÂÂ150 üm thick. The surface is uneven and lacks a , and parts of the thallus may flake away. The photosynthetic partner () is from the green algal genus Trentepohlia (cells 8âÂÂ12 à6âÂÂ8 üm). The medulla is white and contains many clusters of calcium oxalate crystals, and the base includes a strongly (blackened) layer about 30âÂÂ70 üm thick.
The fruiting bodies are that are , densely branched, and often arranged in star-like clusters. They are immersed, 0.5âÂÂ3 mm long and 0.2âÂÂ0.4 mm wide, with a thick white . The exposed is brown-black and lacks . Ascospores are single per ascus, ellipsoid, richly , and measure 80âÂÂ120 à20âÂÂ30 üm; 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.
The species is known from Amazonian Peru (Madre de Dios), where it was collected at about elevation in tropical lowland rainforest, growing on tree bark in secondary forest.