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Minute to small stratified foliose or occasionally fruticose lichens, corticate above and below, sorediate or isidiate or not, lobes closely appressed to loosely attached or semi-erect, short to more often elongate or elongatelinear, averaging to 0.3–1 (–2) mm wide, thin or somewhat thick. Upper surface orange or orangish, K+ purple. Lower surface pale, often whitish, often bearing scattered, short, simple rhizines. Medulla white. Photobiont green.
Apothecia located over upper surface, disc orange; spores 2-celled, ellipsoid, colourless, 8 per ascus.
Over base-rich rock and bark, occasionally over bone.
Notes: Xanthoria is primarily a temperate genus consisting of approximately 15 species worldwide. Ten are reported for North America and six for B.C. The western Xanthoriae are in need of taxonomic revision; therefore the following account is tentative, pending further study. Chemistry is of little taxonomic value in this genus and is omitted.
Soredia and/or isidia present AND Isidia and/or soredia located mostly along lobe margins and/or lobe tips, sometimes also developing on lower surface AND Lobes proportionately rather long and narrow; soredia and/or isidia present, loosely scattered along lobe margins and/or lobe tips; rhizines present or absent; over bark or rock AND Lobes usually averaging to more than 0.2 mm wide; upper surface orange (except sometimes yellowish green in shaded sites), K+ purplish AND Lower surface lacking rhizines
The material included here is apparently heterogeneous, the lobes being short and proportionately broad in some specimens and elongate and distinctly narrow in others. The former specimens resemble X. fallax.
Source: Lichens of British Columbia