Nearly half of British Columbia’s rare tree-dwelling macrolichens have cyanobacterium as photobiont. Such species can be referred to as epiphytic cyanolichens. As a group, epiphytic cyanolichens have a requirement for nutrient- rich substrates with a pH above about 5.0; they tend to be absent from acidic substrates, including the bark of conifers. Viewed from this perspective, the copious presence of cyanolichens over the bark of pines, spruces, hemlocks, and other members of the Pinaceae in some portions of northwestern North America would seem anomalous. We propose that this phenomenon must reflect nutrient enrichment from sources extraneous to the trees themselves. Enrichment may derive, for example, from airborne dust, aerosols associated with the spray zones of waterfalls, or from nutrients present in the soil.