World distribution: Cladonia fragilissima is an oceanic species, known only from western Europe (Østhagen & James 1977, Timdal 1982, Aptroot & Lumbsch 1985, Purvis & James 1992a, Paus 1994), apparently with a center of distribution in the British Isles. In Scandinavia the species is known from Norway and Denmark
Ecology: Results. The substrate (indicated in 4 localities) was horizontal peat (1), a rock face (1), a shaded rock (1), and a moist shelf in a rock wall (1). The habitat (indicated in 4 localities) was coastal heath (1), a Pinus sylvestris forest (1), a Corylus avellana grove (1), and a brook ravine (1). At the time of the investigation, some populations were inundated. Recorded aspects were northern and northeastern. Discussion. Cladonia fragilissima is an oceanic species, demanding microclimatically humid sites, e.g. brook ravines and inundated rock surfaces. When sufficient moisture is available, it is apparently not very substrate specific. In the British Isles, the species occurs on acid, sometimes waterlogged, peaty soils and at the edges of peat hags in lowland and montane heathlands, as well as on mine spoil heaps (Purvis & James 1992a). In Denmark it occurs on small sanddune cuttings in coastal heath (Paus 1994)
Threats: Results. Assumed threats were forestry (1), overgrowth (1), and construction (1). Discussion. Since Cladonia fragilissima occurs in small populations in a few sites only, random extinction is also a threat. The population in Flora (68) is threatened by building on the site
Status: All old sites were investigated. In site 68 the species is still relatively abundant; in site 69 the habitat was still present (but the species sought for); in site 67 the species was not found. One new site was discovered. Thus the species is present with certainty only in two sites: one small, but abundantly fertile population in Hordaland (3227) and one relatively large population (comprising two subpopulations about 50 m apart) in Sogn og Fjordane (68). There are no protected localities
Specimens in other herbaria, litterature, etc.