lichen

/ˈlaɪkən/

/ˈlaɪkɪn/

Other forms: lichens

Have you ever walked through the woods and seen a crusty-looking shelf growing out of a tree? That is actually a lichen, a complex organism comprised of a fungus and its partner algae, the two parts interweaving to form one.

The word lichen appeared around 1600, and was drawn from the Greek leikhēn, meaning "what eats around itself." This is a good meaning for what the word represents, as lichen is comprised of fungus cells that literally surround the algae cells to form a mutualistic bond. Because of the crusty look of a lichen, the name has also been given to a number of skin diseases that present the same patchy look as the fungus-algae.

Definitions of lichen

1. noun

   any thallophytic plant of the division Lichenes; occur as crusty patches or bushy growths on tree trunks or rocks or bare ground etc.
   types:

   ascolichen

   a lichen in which the fungus component is an ascomycete

   basidiolichen

   a lichen in which the fungus component is a basidiomycete

   lecanora

   any lichen of the genus Lecanora; some used in dyeing; some used for food

   Roccella tinctoria, roccella

   a source of the dye archil and of litmus

   Usnea barbata, beard lichen, beard moss

   greenish grey pendulous lichen growing on trees

   horsehair lichen, horsetail lichen

   any of several lichens of the genus Alectoria having a thallus consisting of filaments resembling hair

   Cladonia rangiferina, arctic moss, reindeer lichen, reindeer moss

   an erect greyish branching lichen of Arctic and even some north temperate regions constituting the chief food for reindeer and caribou and sometimes being eaten by humans

   crotal, crottal, crottle

   any of several lichens of the genus Parmelia from which reddish brown or purple dyes are made

   Cetraria islandica, Iceland lichen, Iceland moss

   lichen with branched flattened partly erect thallus that grows in mountainous and Arctic regions; used as a medicine or food for humans and livestock; a source of glycerol

   manna lichen

   any of several Old World partially crustaceous or shrubby lecanoras that roll up and are blown about over African and Arabian deserts and used as food by people and animals

   archil, orchil

   any of various lecanoras that yield the dye archil

   type of:

   fungus

   an organism of the kingdom Fungi lacking chlorophyll and feeding on organic matter; ranging from unicellular or multicellular organisms to spore-bearing syncytia
2. noun

   any of several eruptive skin diseases characterized by hard thick lesions grouped together and resembling lichens growing on rocks
   types:

   lichen planus, lichen ruber planus

   an eruption of shiny flat-topped purplish (usually itchy) papules on the wrist and forearms and thighs

   type of:

   disease of the skin, skin disease, skin disorder

   a disease affecting the skin