General:
Common Name: The Rockfrog Lichens. Suggested by the greenish colour of the upper surface, as well as the strict association with rock surfaces.
Small to large stratified foliose lichens, corticate above and below, sorediate or isidiate or not, lobes tightly appressed to semi-erect, elongate to elongate-linear, averaging to 0.5–5 mm wide, thin to somewhat thickened. Upper surface pale yellowish green, K-, rarely white-maculate, somewhat shiny. Lower surface pale to black, somewhat shiny, bearing scattered short, simple or sparingly branched rhizines. Medulla white (ours). Photobiont green.
Apothecia located over upper surface, disc brown; spores simple, ellipsoid, colourless, 8 per ascus.
Over rock, rarely over soil or moss.
Notes: Xanthoparmelia contains about 400 species worldwide, of which 51 species occur in North America and eight in B.C. Xanthoparmelia is taxonomically the most difficult of the genera previously united within Parmelia. Reliable identification of many species depends on a knowledge of the chemical substances they contain. Though this is most reliably attained through use of thin-layer chromatography, the chemistry of the B.C. Species can usually be surmised from the medullary reaction with K. Two character states are recognized: K+ finally reddish orange or orangish red (i.e., salazinic acid present), and K+ finally yellow or medium orange (stictic acid present). The distinction between these two reactions can be subtle, depending on the concentration of the chemical substances. In difficult cases, intensify the reaction by applying a second drop of reagent to the test site.

Species description:
Thallus lacking soredia and isidia AND
Lobes elongate to elongate-linear; rhizines usually present; distribution various; medulla KC+ reddish or KC- AND
Lower surface somewhat shiny, not at all white-pruinose; upper surface more or less shiny; distribution various; medulla KC- AND
Lower surface pale tan to brownish (occasionally, however, with scattered black patches); lobes broad to elongate-linear, but usually averaging to more than 1 mm wide; distribution various; common; medulla sometimes K+ finally reddish AND
Thallus loosely attached (rarely unattached), occasionally over soil or moss; peripheral lobes mostly elongate-linear; pycnidia absent or sparse over upper surface; lobe margins often distinctly rimmed (check lower surface); dry southern intermontane; medulla K+ finally reddish orange or orangish red AND
Thallus usually more or less attached; upper surface not at all maculate

Comments:
Hale (1990) states that X. wyomingica is commonly pycnidiate, though the B.C. material rarely produces pycnidia.

Reactions:
Cortex KC+ yellow; medulla K+ finally reddish orange or orangish red, PD+ orangish.

Contents:
Salazinic and usnic acids (and consalazinic and norstictic acids).

Source:  Lichens of British Columbia