Lichens

Lichen-covered rocks at Lake Muir NR

About Lichens

Lichens are biologically fascinating, ecologically important and surprisingly diverse. They are good indicators of pollution and the health of vegetation. They are also primary colonisers that are able to break down organic and inorganic materials. Lichens are an attractive part of our flora that are often overlooked and undervalued.

Lichens form part of a group known as cryptogams. Cryptogams are plants that produce spores instead of seeds. Cryptogams include lichens, mosses, liverworts and alga.

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Lichens are a symbiotic relationship between algae and fungi. They sometimes exist apart, but prefer to co-exist. How these two partners 'find' each other is virtually unknown and is one of the mysteries of nature.

A lichen's structure consists mostly of fungus. The fungus provides support and anchorage, absorbs water and helps to obtain mineral nutrients by breaking down surface material. The algal (or cyanobacterial) partner photosynethises, converting energy from the sun to produce food for both partners. In some cases, lichen have more than one type of algal partner.

There are approximately 20,000 species of lichens in the world. Australia has around 2820 species of lichen, 2000 of which occur nowhere else on earth. Western Australia has around 720 species, 10% of which are endemic.

Lichens grow in widely diverse habitats. Lichens grow in rainforests, dry sclerophyll forest, semi-arid soil, stony deserts, desert scrub, alpine high plains, mangrove swamps and coastal heath. Lichens also grow on a variety of surfaces such as trees, rocks, charred wood, mosses, soils, walls and man made surfaces including old car bodies, broken glass, china, and the roof tiles of older houses. Some lichens can obtain all their food and mositure from the air. Other lichens use chemical etching to digest their host material. There are lichens that can tolerate extremely harsh conditions and exposure to the elements. Other lichens prefer secluded niches.

In long dry periods lichens can dehydrate and go into a resting phase. On rewetting they will resurrect and hydrate back to their former living state. An example of resurrection lichen is Xanthoparmelia semivirdis which grows from semi-arid areas in the wheatbelt fringe to arid areas of inland Western Australia. This common species turns yellow and rolls up when dry and unrolls and turns green when re-hydrated.