Nature Notes – For the Love of Lichens

When you’re out and about in the hills and mountains at this time of year, you would be forgiven for thinking the brown, bare and seemingly lifeless hillsides offer little to see in the way of wildlife, but think again, you are surrounded by some of the most fascinating living organisms on Earth, the lichens.


Lichens are everywhere in the outdoor environment, they give colour and texture to much of the bare rock in the mountains, to tree bark in the woods, and to fence posts, graveyards and walls in the countryside.


They are ubiquitous, but largely ignored. So here are 10 things you probably didn’t know about lichens:

  1. Lichens occupy around 8% of the land surface of the Earth. They are often the first species to occupy bare rock, and act as a source of nitrogen for other species, such as birds. They are an essential component of many food chains.
  1. They are a composite, symbiotic organism, comprising a fungus, (a bit like bread mould), and an algae, (related to seaweed). Sometimes they are combined with a third organism, cyanobacteria. The fungi give protection and support, whilst the algae and cyanobacteria are photosynthesizers and produce food from water, carbon dioxide and sunlight.
  1. Ireland is very rich in lichens, having over 1,160 recorded species. There are around 20,000 lichen species on the Earth.
  1. Lichens fall into 4 basic types. Crustose, which form a crust on surfaces like rock and bare metal. Foliose, which have a distinctive upper and lower surface, and resemble foliage. Fruticose, which take the form of cup lichens (pixy cups), bearded (old man’s beard) and shrubby lichens (reindeer moss). And finally, Squamulose, which take scale or plate like form.

    Crustose lichen, possibly Ophioparma, clinging to bare granite rock.

  1. Lichens grow very, very slowly, less than 1mm a year, and a believed to be some of the longest living organisms on the planet, some have been found to be 4,500 years old.
  1. Lichen like forms of life have been identified in the fossil record as far back as 600 million years ago.
  1. Most lichens are very vulnerable to air pollution, as they absorb heavy metals from their environment. This makes them good indicators of pollution levels, and in this way they act as biomonitors.


    A foliose lichen, with its leaf like structure.

  1. Lichens with known growth rates have been used to date geological events, such as the retreat of glaciers in the North American arctic.
  1. Lichens are able to shut down their metabolism during periods unfavourable to growth, such as extreme heat, cold and drought.
  1. Having adapted to life in marginal habitats, lichens have produced more than 500 biochemical compounds, some of which have been used as dyes, poisons and medicines by traditional native societies. Today they are used in the perfume industry.



Cladonia coccifera and Cladonia diversa, Pixy cup and Devil’s matchstick lichens. These are both fruiticose forms.


If you want to discover more about lichens, and specifically those found in Ireland, join one of our Wicklow guided hikes this winter at:

If you wish to read more, check out ‘ Lichens of Ireland’ – by Paul Whelan (Collins Press)

Or go to his website:

About Author

Russell is the founder and owner of With over 35 years of mountaineering experience, including expeditions in Europe and Africa, Russell leads many of the trips himself, and is a fully qualified Mountain Leader, has a Rescue and Emergency Care First Aid qualification and is fully insured.


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