Lichens are composite organisms consisting of a fungus (the mycobiont) in a stable association with a photosynthetic alga or cyanobacterium (the photobionts). As there is often more than one photobiont and a number of other micro-organisms involved e.g. bacteria, yeasts and lichenicolous fungi; lichens are more like an ecosystem than an individual species. The relationship between the various partners is complex and may involve elements of symbiosis, commensalism and parasitism. Therefore, it is not that surprising to discover that lichens are found in a wide of range habitats and ecological niches, and are morphologically and biochemically diverse.
There are about of 1500 species of lichens in Scotland, but so far only 650 species have been recorded in the Outer Hebrides. This lack of diversity arises from the combination of geological uniformity (almost entirely Lewisian gneiss and associated siliceous rocks) and a limited range of habitats. There may also be an element of under-recording as, until relatively recently, the islands' lichens were recorded by visiting lichenologists.
We have been looking at lichens since 2010, but until relatively recently our focus has been on the macro-fungi. This section of the website contains a catalogue of the species which we have identified and photographed. Information on their distribution is available on the National Biodiversity Network Atlas Scotland website.
Lichens are classified and named according to their fungal component, however, as an aid to identification, lichens are grouped according to their growth form or type. This is an artifical construct as the growth form bears no relationship to the taxonomy of the lichen, but it makes life easier.