Most lichens grow on bare rock, soil or on the bark of trees and shrubs. Their ability to exploit extreme habitats, coupled with the sensitivity of their fungus-alga symbiosis, mean that they not only possess a tangible and important ecological role, but also their diversity and abundance are reliable biological indicators of overall environmental health.
Lichens colonise bare rock, over time breaking down the substratum and beginning the process of soil-formation. In semi-arid and arid Australia, vast communities of soil-inhabiting lichens bind the substratum by means of minute root-like organs, thus reducing erosion. The sensitivity of the lichen symbiosis even to very small levels of pollutants in the air means they are ideal biological indicators of air quality in urban, suburban and agricultural areas.
Lichens are especially diverse in tropical and subtropical rainforest. The structure of lichen communities on the bark and leaves of trees and shrubs is a reliable indicator of forest type and the extent of disturbance. Lichens produce unique secondary compounds. Some have proven pharmaceutical value, and the potential of other species in the diverse Australian lichen flora has not gone unnoticed.
With more than 3200 species currently known from Australia, the lichens are both a diverse and an ecologically important group of organisms.
Structure of Lichens
The main structure on lichen is the body, called the thallus. Lichens are put into four groups according to the shape of the thallus.
- Foliose lichens - flat, leaf-like structure
- Fruticose lichens - bushy structure
- Squamulose lichens - tiny, scale-like squamules
- Crustose lichens - flat crust on or below rocks or under the bark of a tree