1. Hammond P, Beliles RP (1980) Metals. In: Doull J, Klaassen CD, Amdur MO (eds) McMillan, New York, Casarett and Doull’s Toxicology, The Basic Science of Poisons, pp 409–467
2. Hoeg OA (1974) Plants and tradition [Planter og tradisjon]. Universitets vorlag, Oslo, p 751
3. Kursanov AL, D’yachkov NN (1945) Lichens and their practical utilization [Lisajniki i ih praktitseskoe ispol’zo vanie]. Akademia Nauk SSSR, Moskva, p 55
4. Laakso PV, Gustafsson M (1952) The colorimetric determination of usnic acid in the lichen Cladonia alpestris. Suomen Kemistilehti 25B:7–10
5. Llano GA (1956) Utilization of lichen in the arctic and subarctic. Econ Bot 10:367–392