Bryan McAllister’s personal reference notebook
July 30, 2026Short & citedBlog
Civic Viewpoint.
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Field Notes • Biology

Lichen

Lichens are composite organisms formed by a symbiotic association between a fungus and a photosynthetic partner, usually a green alga or cyanobacterium.

Updated July 30, 20261 min readCited sources

Lichens are composite organisms formed by a symbiotic partnership between a fungus and a photosynthetic partner, usually a green alga or cyanobacterium. They are not plants, though they often appear plant-like and thrive in diverse terrestrial habitats worldwide.

What it is

A lichen is a stable mutualism: the fungal partner (mycobiont) provides structure and protection, while the photosynthetic partner (photobiont) supplies sugars via photosynthesis. The fungal hyphae surround the photobiont cells, forming a thallus. Most lichens are ascomycete fungi, with rare basidiolichens.

Key details

Lichens absorb water and nutrients directly from rain and air, lacking roots or vascular tissue. They reproduce sexually through fungal spores or vegetatively when both partners disperse together. Common growth forms include crustose (flat), foliose (leafy), and fruticose (shrubby).

Why it matters

Lichens are widespread across Canada, especially in forests, tundra, and boreal regions. Many species are sensitive to air quality, making them valuable for ecological monitoring. They colonize rocks, soil, and trees, contributing to nutrient cycling and habitat formation.

In short

  • Lichens are symbiotic associations, not single organisms.
  • The fungal partner (mycobiont) dominates; the photobiont provides food.
  • They grow on surfaces worldwide, absorbing water directly.
  • Lichens are used in Canada for air quality monitoring.
Canadian angle

Lichens are widespread across Canada, especially in forests, tundra, boreal regions, and rocky habitats, and they are often used in ecological monitoring because many species are sensitive to air quality.

Quick questions

What is a lichen?
A lichen is a symbiotic association between a fungus and a photosynthetic partner, usually an alga or cyanobacterium.
Are lichens plants?
No. They may look plant-like, but lichens are composite organisms made of at least two partners, with the fungal partner dominant.
How do lichens get water?
They absorb water and nutrients directly from rain, air, and their surroundings rather than through roots or vascular tissue.

Sources

  1. Encyclopaedia Britannica — https://www.britannica.com/science/lichen
    Supports: Definition of lichens as symbiotic associations; worldwide distribution; approximate diversity.
  2. U.S. Forest Service — https://www.fs.usda.gov/wildflowers/beauty/lichens/about.shtml
    Supports: Basic lichen biology; fungal dominance; lack of roots, stems, and leaves; water and nutrient absorption.
  3. U.S. Forest Service — https://www.fs.usda.gov/wildflowers/beauty/lichens/biology.shtml
    Supports: Lichen structure, absence of vascular tissue, and environmental absorption of water and nutrients.
  4. U.S. Fish & Wildlife Service — https://www.fws.gov/story/2023-12/lichen-what-fungus-it
    Supports: Composite organism explanation; photobiont role; fungi-algae/cyanobacteria partnership.
  5. British Lichen Society — https://www.britishlichensociety.org.uk/learning/what-is-a-lichen
    Supports: Symbiotic association; photobionts; mutualism; multiple partners in some lichens.
  6. British Lichen Society — https://www.britishlichensociety.org.uk/learning/lichen-biology
    Supports: Reproduction by fungal spores and vegetative dispersal.