E-Flora BC: Electronic Atlas of the Flora of British Columbia

General:
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.

Species description:
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

Comments:
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.