Substrate and ecology: on non-calcareous rocks (basalt, granite, sandstone), occasionally on soil, rarely on bark (Pseudotsuga); often in dry, sunny localities, moderately nitrophilous, in our area occurring in desert, grassland, chaparral, coastal scrub, or Douglas fir forests; in Europe described as orophilous; World distribution: alpine to Mediterranean, Europe, Asia, and North America (mostly along the west coast, north to Alaska); Sonoran distribution: southern California at 50-650 m.; Notes: This subspecies can be distinguished from the typical one when growing side by side, as in Weber s-1743 (COLO) from Ventura Co., especially by the somewhat thicker and coarser (mostly 4-6 mm long and 1-1.5 mm wide) lobes. According to Poelt (1958) and subsequent literature, it has a somewhat different ecology and distribution (mostly acidic rocks, in Europe occurring mostly away from human-influenced areas). The isotype (M!) is rather thin, tightly attached, and strongly black-edged, with rather dark brown discs, but material determined by Poelt as var. or subsp. dubyi is much more variable than suggested by his 1958 key (e.g., the discs are often pale yellow, the lobes are often somewhat concave, etc.). Material from British Columbia and Alaska often becomes very thick and almost foliose, and may be a distinct taxon. Numerous specific and infraspecific names applied in Eurasia may be synonyms.
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