World distribution: The species occurs in the eastern U.S.A., Central and South America (Hale 1975), East Africa (Swinscow & Krog 1988), and New Zealand (Galloway 1985). In Europe it is a strongly oceanic species that occurs partly near the Atlantic coast in France, in the western parts of the British Isles (Seaward & Hitch 1982), and partly in humid forests in the most oceanic northern parts of the Alps (Schauer 1965). In Scandinavia it is restricted to Norway
Ecology: Results. The species has been collected on moss covered rock (10 records, mainly rock walls), and on bark of Betula sp(p). (4), Alnus glutinosa (2), Juniperus communis (1), Populus tremula (1), Quercus sp(p). (1), Sorbus aucuparia (1), and on wood of Juniperus communis (1). The habitats were Betula forests (5), Alnus glutinosa forests (2), thermophilous deciduous forests (2), a Populus tremula stand (1), pastures (2), and different types of rocky habitats (3). Recorded aspects were northern (8). Bryoria bicolor and B. smithii were often mentioned as associated species. Discussion. Hypotrachyna laevigata seems to have a stronger preference for rock in Norway than in the British Isles (cf. James et al. 1977, Purvis & James 1992c). It seems to have a preference for rock in forested habitats. It is a hyperoceanic species, in the British Isles mainly restricted to areas with at least 1270 mm annual rainfall and over 180 rainy days which leaches the bark to pH 3.7-4.6 (James et al. 1977). The altitude appears to be less important than exposure to rain-bearing winds (James et al. 1977). The species seems to be sensitive to SO2-pollution, but is apparently increasing locally in western Scotland (Seaward & Hitch 1982). Day (1985) reported that H. laevigata was abundant on the acidified bark of trees in Cumbria. The species seems to be among the lichens that are the least sensitive to low pH, showing a minimal leakage of K under experimental low pH conditions (Farmer et al. 1992). James et al. (1977) have named the 'Parmelion laevigatae' after this species. This assemblage occurs on acid bark in well-lit forests, but H. laevigata has also been noted among the 'Lobarion' assemblage, under constantly wet conditions (James et al. 1977). In Norway it has been observed on bark in relatively young and open forest
Threats: Results. Recorded threats include forestry (7), building on the site (2), abbrasion and collecting (2), and closure of forests (1)
Status: Six old localities were investigated; it was found in 2 localities, regarded as extinct in 3, and of uncertain status in 1. It was found in 6 new localities. It was abundant in 6 localities. On site (308), the species was recorded on 30 Betula pubescens trees, 4-5 Juniperus communis trees, and on 4 rock walls. This site is within a nature reserve, and the only protected locality for the species
Specimens in other herbaria, litterature, etc.