Lichens are dual organisms; a fungus and one or more algae in a stable, mutually beneficial (symbiotic) partnership. The fungus provides structural form and protects the algae from extremes of light and temperature. Algae are capable of photosynthesis and some of the sugars produced provide the fungus with energy for growth and reproduction. Some lichens can live for many hundreds of years and being sensitive to pollution levels they are important enviromental indicators.

Lichen identification can be very confusing to begin with as there are many similar species but the first step is recognising the different growth forms shown below and the reproductive features; apothecia (fruiting bodies), isidia (tiny outgrowths) or soredia (often sperical and powdery). These and the habitat are important details that aid identification. (Glossary)
Photographs are useful but often can't provide an accurate identification as this can require a hand lens, simple chemical tests, examination of the spores using a microscope or even Thin Layer Chromatography.

Please use the menu bar or the links below to see lichens by growth form, habitat or access species with the A-Z Index.

Crustose, Leprose               Squamulose                   Foliose                       Cladonia           Fruticose, Filamentous
Crustose and Placodioid lichens Squamulose lichens Foliose and Squamulose lichens cladonia species Fruticose and Filamentous lichens
The Burren (limestone)     Acidic uplands     Coastal     Urban, churchyard     Trees, wood     'Western oceanic'

For photographs of Fungi, lichenicolous fungi and algae, seaweed, slime moulds and galls please follow the links.
Photographs and details of Wildflowers, Grasses, Sedges and Rushes found in Ireland are at

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