World distribution: It occurs in northern, central and southern Europe, northern Africa, central Asia, and western North America (Arizona to Alberta). There is a single Swedish locality (Södermanland), but it is not known from Denmark or Finland
Ecology: The species grows on steep, often overhanging, rock walls, usually exposed but sometimes in moderate shade. The substrate is exclusively calcareous rock, mostly limestone. It apparently always starts growth as a parasite on cyanophilic lichens, especially Collema spp
Threats: There are probably few threats, except possibly land development (limestone quarries, road construction, etc.) and local air pollution (observed in Porsgrunn, Telemark)
Status: The Norwegian population is small, c. 25 localities are known. There is no indication of any increase or decrease (except depauperate specimens in one locality in Porsgrunn; probably caused by local air pollution)
Notes: The species is usually accompanied by a rich xerophilic lichen flora, reminiscent of that of Mediterranean limestones. The very small areas occupied by this species are valuable for the conservation of local biodiversity, and the species may be used as an easily identified indicator of such sites.
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