Opegrapha is a genus of mostly lichen-forming fungi in the family Opegraphaceae. These lichens form crusty patches on bark, rock, or other lichens, and are easily recognised by their distinctive black, slit-like or rounded fruiting bodies that look like tiny scribbles or dashes on the surface. The genus includes about 150 accepted species found worldwide, with most partnering with orange-pigmented green algae, though some live as parasites on other lichens. Opegrapha species are distinguished from similar genera by their combination of branched internal filaments, ascospores with multiple septa, and a specialised spore-release mechanism.

Opegrapha has a cosmopolitan distribution, occurring in both temperate and tropical regions, though the genus is especially diverse in warm, humid climates. Most species grow on tree bark in shaded woodlands, while others colonise sheltered rock surfaces. The genus is sensitive to environmental conditions and serves as an indicator of air quality: many species declined dramatically during periods of industrial sulfur dioxide pollution but have rebounded in regions where emissions have been reduced, with formerly rare species now increasingly encountered on city trees and in parkland. Around seventy species are lichenicolous, growing parasitically on specific host lichens rather than forming independent thalli, and these forms can indicate ecological continuity as they require stable, undisturbed habitats where their hosts flourish.

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