A lichen is a complex, symbiotic organism composed primarily of a fungus living together with photosynthetic partners, which are usually green algae or cyanobacteria. This partnership forms a stable, mutualistic relationship where the fungus (called the mycobiont) provides structure and protection, while the algae or cyanobacteria (called the photobiont) conduct photosynthesis to produce nutrients like sugars that feed the fungus
. Lichens are not single organisms but rather a composite of multiple species living as one. They often include additional microbes such as yeasts and bacteria embedded in their outer layers. The visible body of a lichen, called the thallus, is made mostly of fungal filaments intertwined with the photosynthetic cells
. Lichens come in various shapes and forms, including:
- Crustose: crust-like, tightly adhering to surfaces
- Foliose: leaf-like and flat with distinct top and bottom sides
- Fruticose: bushy or shrubby, sometimes hair-like or hanging
They grow on diverse substrates such as tree bark, rocks, soil, and even man- made surfaces. Lichens are ecologically important for nutrient cycling, serve as food and habitat for various animals, and are sensitive indicators of environmental health, especially air quality
. In summary, lichens are unique composite organisms formed by a fungus and photosynthetic partners living together in a mutually beneficial relationship, resulting in life forms that are distinct from either partner alone
