Lichens

LICHENS, lichen, Lichenes, a distinctive class of lower plants consisting of a fungus and an alga that form together a single organism. The fungi of lichens, with negligible exceptions, belong to the Ascomycetes. The algae of lichens bear the old general name gonidia. Being unable to tolerate soot and smoke of large cities, lichens are indicators of air purity. In communal living, shrub-like lichens are often incorrectly called mosses. In medicine, only Iceland moss (see) and Lobaria pulmonaria, accepted in the Portuguese pharmacopoeia, are used. Previously, Peltigera canina was used against hydrophobia (pulvis antilyssus), Pertusaria amara in fevers, and others. In the 15th-16th centuries, when the doctrine of 'signatures' was widespread, Usnea barbata, hanging in long strands from trees, was used for hair growth; Peltigera aphthosa, covered with warts, was used for rashes in children; Parmelia saxatilis (muscus cranii humani) growing on human skulls was used for epilepsy, etc. Apparently only two lichens are poisonous: Letharia vulpina and Cetraria pinastri; the first is used in the north for poisoning wolves.