English: Dog lichen (Peltigera canina) This is a common lichen most often seen in the winter when damp conditions plump up its thalli - the grey leaf-like structures seen here. In drought they curl up like paper. It is to be found on rocks and dead wood, often growing in some profusion. It also occurs on lawns and grasslands where there is poor drainage.

The brown capsules, or apothecia, seen here at the tips of some of the thalli contain the spores. The lichen's specific name, canina, (although it is now thought this common species should correctly be referred to as P. membranacea) relates to the resemblance of the white pointed spikes on the underside of the thallus to the fangs of a dog. Accordingly, by the doctrine of signatures, the lichen was once recommended as a cure for rabies.

"In the words of John Lightfoot: The L. caninus has a disagreeable musty taste. Half an ounce of the leaves, dry'd and pulveriszed, and mixed with two drachms of powdered black pepper, compose the once-celebrated Pulvis antilyssus, formerly much recommended by the great Dr. Mead, for the cure of canine madness. This medicine was to be divided in four equal parts, one of which was to be taken by the patient every morning, fasting for four mornings successively, in half a pint of warm cow's milk; after which he was to use the cold bath every morning for a month. It is much to be lamented that the success of this medicine has not always answered the expectation. There are instances where the application has not prevented hydrophobia; and it even uncertain whether it has been at all instrumental in keeping off that disorder."

Peltigera canina has also been used for a yellow dye.

There is a species of moth (Thumatha senex)whose larvae feed upon it.