Lichens

LICHENS

Lichens are never pathogenic but are important to the ecosystem. They are not a single organism but are a combination of two organisms—a relationship between green algae and cyanobacteria. They break down rock to make soil and some will fix nitrogen and stabilize soil. There are antibacterial properties to some lichens that make them medically interesting.

The relationship between fungi and lichens is partly mutualistic and partly parasitic. It is partly parasitic because the photosynthetic component does not grow as well with the fungus but it can still grow. Lichens themselves grow slowly and may survive for centuries. They can be used as a food source or to make dyes. They are environmental indicators because they die off if there is too much pollution.

The thallus or body of the lichen has an outer cortex made of tightly packed fungi and a medulla made of loosely packed fungi. Rhizines are the hyphal bundles that attach the organisms to the substrate. Figure 26 shows what a lichen looks like:

Figure 26.

Together, lichens are considered fungi. There are crustose lichens that are crusty in appearance, foliose lichens, which are leaf-like in appearance, and fruticose lichens, which have a more rounded appearance and can look branched.