Occurrence
In the lichens, Evernia furfuracea (L.) Mann and Usnea harhata (L.) Wigg (Fam: Usneaceae), found on the bark of fir and pine trees (Guenther, 1952). The lichens include a large number of species, many of which have been studied with regard to their composition and properties (Kjellman. 1957). By selective extraction, several classes of lichen substances can be separated, accounting for 1-8% of the dry weight of lichens and including fatty acids, lactones, triterpenoids, polyhydric alcohols and aromatic substances such as depsides, depsidones, quinones and derivatives of pulvic acid, xanthone. dibenzofuran. and diketopiperazine (Mitchell & Armitage. 1965). One of the most important and widely distributed of the lichen acids is usnic acid, a dibenzofuran first isolated from Usnea harhata. which occurs in considerable quantities in a wide variety of species (Savich. Litvinov & Moiseeva. 1960). Lichen polysaccharides are isolated chiefly from the aqueous extracts (Shibata. Nishikawa. Tanaka, Fukuoka & Nakanishi, 1968c).
Preparation
By extraction of the moss, twigs and needles with volatile solvents and their subsequent removal, usually under vacuum.
Definition
Extractives and their physically modified derivatives. Evernia furfuracea and Usnea barbata, Usneaceae.
Toxicity evaluation
The acute oral LD
50 in rats was reported as 4.33 ml/kg (4.01-4.68 ml/kg), and the acute dermal LD
50 in rabbits exceeded 5 g/kg (Levenstein, 1974). Lichen substances appear to be non-toxic to reindeer and other animals that consume large amounts of lichens in their normal diet (S?derberg, 1953).
Hazard
Low toxicity by ingestion and skin contact.
A mild skin irritant.
