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 sorediate or isidiate AND
Thallus sorediate AND
Lower surface usually somewhat shiny, not at all white-pruinose; upper surface shiny or dull; medulla KC+ reddish or KC- AND
Broadest lobes averaging to less than 1.5 mm wide; rhizines rarely, if ever, branched AND
Upper surface generally shiny throughout, transversely cracked when mature; coastal; over rock; medulla K+ finally yellow to medium orange, PD+ pale orange

Reactions:
Cortex KC+ yellow; medulla K+ yellowish, PD+ orangish.

Contents:
Constictic, norstictic, stictic and usnic acids.

Source:  Lichens of British Columbia