Lichen
Description
Lichens are composite organisms arising from a symbiotic relationship between fungi (mycobiont) and photosynthetic partners, usually algae or cyanobacteria (photobiont). They can grow on a variety of surfaces, including tree bark, rocks, soil, and even man-made structures. Lichens do not have roots but absorb water and nutrients from the air, making them highly sensitive to environmental changes.
They exhibit a wide range of colors, including green, yellow, orange, gray, and black, depending on the species and environmental factors. Lichens grow in diverse forms, generally classified into crustose (crust-like), foliose (leaf-like), and fruticose (shrub-like or branched) types.
Identification
Growth Forms
- Crustose Lichens: Form a thin, tightly attached crust on surfaces, often difficult to remove.
- Foliose Lichens: Have a leaf-like appearance with lobes that can be lifted from the surface.
- Fruticose Lichens: Appear as branching or bushy structures, sometimes hanging like strands.
Colors & Surface Texture
- Can be smooth, powdery, granular, or lobed.
- Often vibrant when wet but dull when dry.
- Some species fluoresce under UV light.
Habitat
- Found in forests, tundras, deserts, and urban environments.
- Thrive in areas with clean air but some tolerate pollution.
Spread
Lichens reproduce through asexual or sexual means.
- Asexual Reproduction: Small fragments (soredia or isidia) break off and are dispersed by wind, water, or animals.
- Sexual Reproduction: The fungal component produces spores, which must re-establish a symbiotic relationship with algae or cyanobacteria to form a new lichen.
Similar Species
- Mosses (bryophytes) may resemble lichens but have root-like structures and do not form fungal symbioses.
- Algae can appear as green films but lack the fungal component of lichens.
- Liverworts, which can have a similar flattened growth, are non-symbiotic plants.