Fungus
Lichen
various — composite organisms
Also known as: lichens
Not a single organism but a *symbiotic composite* — a fungus (typically an ascomycete) living in obligate partnership with one or more photosynthetic partners (typically a green alga or a cyanobacterium). The fungal partner provides structure and water/mineral acquisition; the photosynthetic partner provides carbohydrates via photosynthesis. Together they form one of the most successful symbiotic life-forms on Earth — lichens grow on bare rock in Antarctica, on Arctic tundra, on tropical rainforest tree trunks, on cathedral stones, on cemetery headstones, on roof shingles. Approximately 20,000+ named lichen species exist; the same fungal species may form different lichens with different photosynthetic partners.
Scientific
Lichens are not classified as a single biological group because they are not a single biological entity — each lichen is a composite of a fungus (typically an Ascomycete, sometimes a Basidiomycete) and one or more photosynthetic partners (a green alga or a cyanobacterium, sometimes both).
The fungal partner is called the mycobiont; the photosynthetic partner is called the photobiont. The same fungal species can form different lichens with different photobionts; the same alga can partner with different fungi. The relationship is generally obligate for the fungus and facultative for the alga.
Approximately 20,000 lichen species (technically, lichenized fungi) are named, with new species continuing to be described. Major growth forms include:
- Crustose lichens — flat, tightly attached to substrate; the rock crusts of weathered stone and old bark
- Foliose lichens — leaf-like, with a clear upper and lower surface; only attached at specific points
- Fruticose lichens — branched, three-dimensional, often hanging from trees or growing upright
Ecological and cultural significance
Lichens are pioneer species across nearly every habitat on Earth. They colonize bare rock, contributing to soil formation over [[deep-time|geological time]]. They are among the very first organisms to recolonize habitats after disturbance (volcanic eruption, glacial retreat).
The species’ sensitivity to air pollution — particularly sulfur dioxide — makes them excellent biological indicators of air quality. Many cities and regions in the 1970s–1990s saw dramatic lichen decline correlated with industrial pollution, then gradual recovery as Clean Air Act-style regulations reduced emissions. Tree-trunk lichen diversity is a standard ecological metric of regional air quality.
Cultural uses:
- Reindeer/caribou food — Cladonia lichens are the principal winter food for caribou and reindeer across the Arctic; “reindeer moss” is actually a lichen
- Dye sources — historic European textile dyes from Roccella and other lichens (the source of orchil and litmus)
- Traditional medicine — Usnea and other lichens in traditional pharmacopoeias
- Food — Lecanora esculenta (the “manna of heaven” of some Middle Eastern traditions); various Japanese iwatake lichens
The Antarctic continent is dominated below the ice by extremophile lichens — they survive temperatures below -50°C, prolonged complete dryness, and high UV exposure that no plants tolerate.
See also
Auto-generated from this entry’s typed relations: frontmatter, grouped by relation type so the editorial signal isn’t flattened.
- Shares approach with: [[british-soldier-lichen]] · [[mycorrhizal-fungi]] · [[eastern-red-cedar]] · [[eastern-cottonwood]]
- Member of: [[fungus]]
Sources
- Wikipedia — Lichen
A fungus entry in the 0mn1.one [[directory]].
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