Based on a survey of 935 herbarium specimens collected from British Columbia, the substrate ecology and "lifezone" distribution of 48 species of epiphytic cyanolichens are broadly summarized. Conifers belonging to the Pinaceae provide habitat, in coastal regions, for at least 43 cyanolichen species, 12 of which occur exclusively on conifers. Hardwoods support a similar number of cyanolichens, but provide exclusive habitat for only four species. Cyanolichen diversity on conifer branches is shown to increase along a gradient of increasing summer precipitation. It is suggested that the occurrence of cyanolichens on conifer branches (i.e., the "CC phenomenon") was formerly well developed in many parts of Europe, but has declined in response to increasing acid precipitation. According to this hypothesis, existing epiphytic lichen assemblages in Europe no longer express their full pre-industrial ecological amplitude. In contrast, conifers in Pacific North America apparently still support "pristine" epiphytic communities; this region should be accorded special emphasis for global cyanolichen conservation. The CC phenomenon may offer a highly sensitive early warning system of broad-scale acidification in eastern North America and other regions where industrial activity is increasing.