We found some very fine specimens of dog lichen Peltigera sp. when we were out walking at Shittlehope Burn at Stanhope in Weardale this morning. I've often wondered why it's called dog lichen - I've found one or two references that suggest that Linnaeus gave it the Latin specific epithet caninus because he saw some resemblance to a dog in its shape, which I find hard to see, unless it relates to the menacing tooth-like structures, called rhizines, on the underside of the thallus.
The arrangement of the rhizines, which are extensions of the fungal part of the symbiotic partnership between alga and fungus that constitutes a lichen, are key identification features and as soon as I can get my hands on a lichen field guide I'll try to identify the species more accurately.
Some Peltigera species contain cyanobacteria that fix nitrogen in the symbiotic partnership, so the organism then has its own in-built nitrogen fertiliser supply and plays a part in the cycling of nitrogen in ecosystems.
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