The most commonly occurring cyanobacterium genus is "Nostoc". Other common cyanobacterium photobionts are from "Scytonema". Many cyanolichens are small and black, and have limestone as the substrate. Another cyanolichen group, the jelly lichens of the genera "Collema" or "Leptogium" are gelatinous and live on moist soils. Another group of large and foliose species including "Peltigera", "Lobaria", and "Degelia" are grey-blue, especially when dampened or wet. Many of these characterize the Lobarion communities of higher rainfall areas in western Britain, e.g., in the Celtic rain forest. Strains of cyanobacteria found in various cyanolichens are often closely related to one another. They differ from the most closely related free-living strains.