World distribution: Hypotrachyna sinuosa is widely distributed in tropical and temperate regions (Hale 1975), being known from Europe, South and North America, southeastern Asia, and New Zealand (Galloway 1985). In Europe it occurs in oceanic sites from Portugal (Tavares 1945) to Norway, and in moist parts of the Carpathians and the Alps (Schauer 1965). In Fennoscandia it is restricted to Norway
Ecology: Results. The substrate (indicated in 7 localities) includes bark of Alnus glutinosa (4), Sorbus aucuparia (2), Betula sp. (2), and the smooth bark of a young Fraxinus excelsior (1). On Alnus glutinosa it sometimes occurred exclusively on the smooth bark of the branches. The habitat (indicated in 4 localities) included Alnus glutinosa swamps (2 sites), open maritime A. glutinosa woodland along a main road (1), and grazed Betula forest in the agricultural landscape (1). In a dense Alnus glutinosa forest (1477), it was observed only on well-lit trees along a path. Discussion. Hypotrachyna sinuosa is corticolous on deciduous trees. Alnus glutinosa appears to be its main substrate, but the species may be abundant and very well-developed on smooth bark of Fraxinus trunks. Its frequent occurrences on twigs and smooth bark indicate that it is a pioneer lichen. Apparently, the species cannot tolerate too much shade. In the British Isles it occurs on siliceous rocks, well-lit, acid barked trees (especially on twigs and young branches), and occasionally on wood and stems of Calluna vulgaris (Purvis & James 1992c). In the Alps the species is strongly hygrophilous, being especially well-developed near waterfalls (Schauer 1965) where it may even occur on thin Picea twigs associated with, e.g., Normandina pulchella and Pannaria conoplea. In the Alps, Hypotrachyna sinuosa occurs in similar habitats as those of Parmotrema arnoldii (Schauer 1965). In the British Isles it is characteristic of twigs of broad-leaved trees in more or less continuously humid and moderately exposed, cool sites, with more than 180 rain days per year (Seaward & Hitch 1982)
Threats: Results. In the three investigated sites where the species was found, recorded threats are planting of Picea (1479, 1597), and outshading due to natural succession on previously more open land (1477). In 1477, where the species only was observed along a path, abrasion was considered a possible threat. Site 1595 in Ølen, where it is regarded as extinct, is a roadside bank; the population may here have suffered from pollution from cars
Status: The species was first collected in Norway in 1971 (Østhagen 1971). In subsequent years the species has been found in 6 additional sites (Tønsberg 1979, 1980, Timdal 1982). All sites were investigated. The species was found in 3, assumed extinct in 1, and of uncertain status in 3. In Lindås (1597), about 20 thalli were observed on Alnus glutinosa and Fraxinus excelsior, in the two other sites (1477, 1596), which both are within nature reserves, the species was very sparse. No new sites were detected during the investigation
Specimens in other herbaria, litterature, etc.