Lich. Lapp. Orient. 8: 121 (1866).

Basionym: Lichen ambiguus Wulfen, in Jacquin, Collectanea Bot. 4: 239 (1791) [1790].

Thallus forming rosettes, closely adnate, often growing together in large patches, to 5 cm diam., usually smaller; lobes to 1 mm wide, elongate, flat or slightly concave, discrete, sparingly indented and branched towards the tips; upper surface yellow-green, matt; soralia frequent, laminal, rarely capitate; lower surface brown. Apothecia infrequent, to 2 mm diam.; disc brown. Spores narrowly ellipsoid, 6- 12 x 3 μm. Pycnidia common. Conidia filiform, 12-18 x 1 µm. Chemistry: Cortex C—, K+ pale yellow, KC+ yellow, PD—, UV—; usnic acid; medulla K—, KC—, PD—, UV+ white; divaricatic and nordivaricatic acids. Habitat: On bark and wood, often old conifers and fence posts, rarely on rocks. Indicator of snow depth in northern forests (see P. hypenopta). Distribution: Common throughout the forests of the Nordic countries, extending to dwarf shrubs in alpine and arctic areas.Widely distributed in temperate-boreal areas of the Northern Hemisphere, also known from Australia. In eastem North America much less frequent than the similar P. capitata and P. subambigua with capitate and postulate soralia respectively.