The thallus of Peltigera canina is large and foliose, forming extensive mats with each lobe reaching at least 1 cm wide. The diameter of the entire thallus can reach up to 20 cm across. The upper surface is brown to greenish brown when wet and turns a frosty gray when dry due to the tomentum on the surface, the thallus margins undulating in a wave. The lower surface has white veins and dense, branched, hairlike rhizines. The apothecia are reddish brown and form at the lobe margins on separate raised narrow lobes. P. canina is one the lichens forming an association with Nostoc, a blue green algae as opposed to a green algae.
P. canina can be found using soil, moss, the forest floor, rotten logs or soil and moss over rocks as a substrate in forests or recently disturbed areas from low elevations to subalpine conditions. P. canina is very common in open forests east of the Cascade Mountain Range of the Pacific Northwest.
There are three other species of Peltigera that have a tomentose, or fuzzy upper surface P. rufescens, P. membranacea and P. praetextata. The first, P. rufescens, is found on on dry exposed soil and has a white upper thallus surface. The tomentum are very thick and the rhizines come together forming a mat on the substrate, only free at the margins. P. membranacea has a wider distribution west of the Cascades than other look-alikes and the upper surface is less hairy. On the lower surface, P. membranacea has rhizines that resemble ropes more than hariy tufts. P. praetextata has lobules along thallus margins and cracks in the thallus, unlike other similar species of Peltigera. The rhizines are thin and less fibrous and the veins more subtle as well.
The name Peltigera canina has historically been used liberally, therefore the true distribtuion is unknown.
In medieval Europe, P. canina was used to treat rabies in accordance with the populat doctrine of signatures as the erect apothecia were said to look like the teeth or ears of a dog, also leading to the common name of Dog Lichen.
Photo taken in Beazell Memorial Forest near Wren, Oregon.
Brodo, I.M., S.D. Sharnoff and S. Sharnoff (2001) Lichens of North America. Yale University Press, New Haven, Connecticut.
Kozloff, E.N. (1976) Plants and Animals of the Pacific Northwest. University of Washington Press, Seattle and London.
McCune, B. and L. Geiser (2009) Macrolichens of the Pacific Northwest. Oregon State University Press, Corvallis, Oregon.