World distribution: The species, which comprises two varieties, is widely distributed in temperate and tropical areas and is known from South and North America, Africa, Asia, Australia, and Europe (Degelius 1974, Tønsberg 1993). Var. leptaleum is the commonest one with occurrences on all continents, whereas var. biliosum is mainly a tropical taxon not known to occur in Europe. Its world distribution has been mapped by Degelius (1974). In Europe the species is only known from Norway (Tønsberg 1993)
Ecology: Results. Collema leptaleum has been found on bark of pollarded trunks of Fraxinus excelsior in a Fraxinus-Quercus grove in a south-facing slope in an old cultural landscape. The species occurred on naked bark mainly on the south-facing side of the trunks, partly also on the lower side of slightly leaning trunks. Associates included Acrocordia gemmata, Bacidia rubella, Collema flaccidum, C. nigrescens, Gyalecta truncigena, Leptogium saturninum, L. teretiusculum, Melanelia glabratula, Nephroma resupinatum, Opegrapha rufescens, Parmeliella triptophylla, and the bryophyte Leucodon sciurioides. Discussion. Collema leptaleum is probably a warmth-demanding species of eutrophic bark in Norway, possibly preferring habitats influenced by man. According to Degelius (1974, 1986), C. leptaleum usually grows on naked bark on trunks and branches of various, particularly broad-leaved, trees, in moist to dry forests, groves, and on solitary roadside trees
Threats: Results. No apparent threat recorded. Discussion. If the trees remain unpollarded, however, they may easily be uprooted by strong winds. Random extinction is a general threat for such small populations
Status: The species grows on at least seven trunks. On some trunks several thalli occurred. The site is not protected
Specimens in other herbaria, litterature, etc.