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Letharia vulpina, commonly known as the wolf lichen (although the species name vulpina, from vulpine relates to the fox), is a fruticose lichenized species of fungus in the family Parmeliaceae. It is bright yellow-green, shrubby and highly branched, and grows on the bark of living and dead conifers in parts of western and continental Europe, the Pacific Northwest and northern Rocky Mountains of Western North America. This species is somewhat toxic to mammals due to the yellow pigment vulpinic acid, and has been used historically as a poison for wolves and foxes. It has also been used traditionally by many native North American ethnic groups as a pigment source for dyes and paints.
The thallus, or vegetative body, has a fructicose shape — that is, shrubby and densely branched — and a bright yellow to yellow-green, or chartreuse color, although the color will fade in drier specimens. Its dimensions are typically 2 to 7 cm (0.79 to 2.76 in) in diameter. The vegetative reproductive structures soredia and isidia are present on the surface of the thalli, often abundantly.
Like most lichens, L. vulpina is highly tolerant of freezing and low temperatures. In one set of experiments, the lichen was able to reactivate its metabolism after 15 hours of cold storage and resume photosynthesis within 12 minutes of thawing. It was also able to start photosynthesis while rewarming, still at below-zero temperatures (°C), suggesting that it may remain active during winter.
L. vulpina prefers to grow in high elevations, just above the tree line in the Pacific Northwest. It is often abundant on exposed branches that have lost their bark. In old, moist forests, it is typically found in drier areas. This species has an intermediate air pollution sensitivity. In the Rocky Mountains, letharia species are found in ponderosa forests at the prairie-forest boundary at relatively low elevations though medium and high elevation Douglas fir and lodgepole pine forests.
The brightly colored fruiting bodies are popular in floral arrangements.
The use of this species for poisoning wolves and foxes goes back at least hundreds of years, based on the mention of the practice in Christoph Gedner's "Of the use of curiosity", collected in Benjamin Stillingfleet, Miscellaneous Tracts Relating to Natural History, Husbandry and Physics (London, 1759). According to British lichenologist Annie Lorrain Smith, reindeer carcasses were stuffed with lichen and powdered glass, and suggests that the sharp edges of the glass would make the animals' internal organs more susceptible to the effects of the lichen poison. However, it is known that the lichen itself is also effective—powdered lichen added to fat and inserted into reindeer carcasses will also be fatal to wolves that consume it. The toxic chemical is the yellow dye vulpinic acid, which is poisonous to all meat-eaters, but not to mice and rabbits.
Letharia growing with Bryoria sp. on pine branches near Blackpine Lake, Washington
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