Lichenology is the branch of mycology that studies the lichens, symbiotic organisms made up of an intimate symbiotic association of a microscopic alga (or a cyanobacterium) with a filamentous fungus. 
Lichens are a complex life form that is a symbiotic partnership of two separate organisms, a fungus and an alga. The dominant partner is the fungus, which gives the lichen the majority of its characteristics, from its thallus shape to its fruiting bodies. The alga can be either a green alga or a blue-green alga, otherwise known as cyanobacteria. Many lichens will have both types of algae.
Growth Forms
There are three main types of lichens:
Foliose Lichens
Foliose lichens have two easily distinguishable sides. In other words, there is a top side and there is a bottom side. They can be very flat, leafy like lettuce, or convoluted and full of ridges and bumps.
Fruticose Lichens
Fruticose lichens can be pendant and hair-like, upright and shrubby, or upright and cup-like. Many fruticose lichens have round branches that have a central core and others are hollow in the middle. Other fruticose lichens have flat branches that tangle up with each other.
Crustose Lichens
Crustose lichens are just that, crusts. They form a crust over a surface, like a boulder, the soil, a car, or your roof shingles. They can come in many bright, vibrant colours like sunny yellow, orange, and red, as well as greys and greens. Crustose lichens are pressed against their substrate.

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