What is a fungus?

Teloschistes flavicans © Chris Cheffings/JNCCFungi belong to a separate kingdom to both plants and animals, and are quite different to both.  It is a large kingdom, with over 15000 species believed to occur within the United Kingdom.  As well as the more familiar mushrooms and toadstools, the fungal kingdom includes a wide range of life-forms including yeasts and pathogens.  Fungi play a large number of roles in ecosystems, and are critical for ecosystem function; for example they are the principal decomposers in many ecosystems, form vital mycorrhizal associations with plants, and provide specialised habitats for a range of other organisms.
The award-winning Checklist of the British and Irish Basidiomycota has been published by Royal Botanic Gardens Kew.  Other groups of fungi lack recent checklists.  The list of fungi used in the Fungal Records Database of Britain and Ireland (managed by the British Mycological Society and hosted by CABI) is also provided to the National Biodiversity Network Species Dictionary.

What is a lichen?

Lichens are stable combinations between an alga and a fungus.  Most of the algae found in lichens can occur as free-growing species, but the fungal partner is never found growing alone.  It is the fungal partner which provides the scientific name for the lichen combination, and hence they are often referred to as ‘lichenised fungi’.  Lichenologists also tend to study lichenicolous fungi; these are fungi that parasitise lichens.
The British Lichen Society maintain a checklist of lichens for Britain and Ireland.  This checklist is also provided to the National Biodiversity Network Species Dictionary.