World distribution: Collema curtisporum is known from Europe and from a few localities in western North America (Montana and Washington) (Degelius 1974, McCune 1982). According to Degelius (1954, 1974) the European distribution is concentrated to Norway, Sweden and Finland, with one additional locality in northern Italy. The highest local abundance is recorded in Jokkmokk, northern Sweden (50 known localities; Karström 1992b)
Ecology: Results. Collema curtisporum is a corticolous species that in Norway so far has been found only on Populus tremula. Recorded habitats were a subalpine Betula forest, a mixed Betula-Picea forest (both Buskerud) and a river gorge with Picea and Pinus (Oppland). The aspect was southern in all sites. Associated species in Buskerud included Pannaria conoplea, while Heterodermia speciosa and Ramalina dilacerata grew in the vicinity of the Oppland locality. All Norwegian localities had a humid microclimate; those in Buskerud in a fog belt, and that in Oppland in a river gorge. Discussion. In Jokkmokk in Sweden the species grows exclusively on Populus tremula, and seems to be restricted to old P. abies forests having a high frequency of P. tremula (Karström 1992b). The high frequency of P. tremula is probably a result of previous catastrophic events; the stands probably represent old successional stages after fires (Karström 1992b). In Norway the smallest C. curtisporum population (41) was within what is likely to be a fire-free refugium, the two richer populations (16, 3260) more likely to have experienced fires
Threats: Results. Assumed threat was forestry (3). Discussion. Clearing represents an important threat as the species probably has a high demand for humidity and/or shade. The only host species, Populus tremula, may show future declines due to recruitment problems within natural spruce forests caused by reduced frequency of forest fires
Status: The single known old locality was investigated and the species found. Two new localities were discovered, one of them a few kilometers from the old one (3260). At this site it was abundant on several trees. At locality 41 it was sparsely represented by a few thalli on one trunk. There are no protected localities
Specimens in other herbaria, litterature, etc.