Looking at Lichens

By June Chatfield

Lichens are curious forms of life that do not fit into one major group of classification, but are stable recognisable partnerships between two groups. The more bulky partner, forming the visible structure of the lichen is always a fungus, but the green photosynthetic powerhouse, making sugars from carbon dioxide and water using solar energy, is usually a green alga but may be a cyanobacterium (previously known as blue-green algae).

Lichens are sensitive to air pollution and need moisture so they are more prolific and varied in the western half of the British Isles: head for the rocky shores, woods and moors of Devon but you will find lichens around your own area and possibly on your roof. Look for lichens on trees, rocks, sandy heaths, buildings and churchyards. There are currently illustrated identification books, a CD Rom lichen identifier, laminated colour field cards and courses run on lichens at the Field Studies Council to help naturalists study this group. Enthusiasts can also join the British Lichen Society.

For many years lichen zones have been used to assess the level of air pollution. With improvements in the quality of air in the latter part of the twentieth century, reducing soot and sulphur dioxide emissions, lichens are making a dramatic come-back in urban and suburban areas. This trend of re-colonisation can be recorded by enthusiastic naturalists.

Shapes and sizes

Lichens vary from tiny particles of loose powder, to crust lichens firmly attached to a hard surface (crustose), flat leafy lobes of lichens that can be picked off (foliose) and erect or hanging branched lobes or cups (fruticose or shrubby lichens). The more complex structures are usually larger. While the small microlichens require specialised study, many of the larger or macrolichens can be confidently recognised and their study enjoyed by the naturalist in the field.

 


Hypogymnia. Photo © June Chatfield


A fence post in the clean air of the Coed-y-Brenin Forest, north Wales with a tuft of shrubby and foliose lichens. Photo © June Chatfield

Where to look for lichens

Species of lichens are often restricted to particular habitats, so searching many types of habitats in an area will reveal the greatest variety of species.

Trees
Many lichens live on trees in woodland, edges of forest rides, isolated trees in parks, roadsides, river banks and gardens. As the green partner has its light filtered through the fungus threads, not all of it penetrates. Lichens therefore need a higher level of light than mosses and they are normally found on the south (sunny) side of a tree trunk. As well as the accessible trunks, lichens colonise branches and twigs of the upper canopy. Samples of these might be brought to the ground with branches after high winds. A new key is now available from the FSC for the identification of lichens on twigs. Lichens living on trees are described as corticolous, an important feature used in identification keys. Having their own system of food production, lichens are not parasitic on trees and they merely use them for support and a high position to retain their place in the sun.


Ochrolechia parella on churchyard wall. Photo © June Chatfield
Pertusaria amara on Brendon Hill. Photo © June Chatfield

Rocks and soil
Another range of lichens live on stone and these are called saxicolous. Apart from ground-living lichens on heathland (usually shrubby lichens of the cup-lichen genus Cladonia) and on steep shaded earth banks (the blue-green powdery Lepraria incana) those of natural rock outcrops are limited to sea cliffs, upper levels of rocky shores, abandoned quarries and mountains. A folding chart is available for lichens of the rocky shore.

Man-made habitats
Human activities provide many suitable artificial surfaces for lichens, including roofing tiles, cement, asbestos, tarmac and walls of gardens and buildings. Tombs and gravestones in churchyards and cemeteries provide habitats for a good range of lichens. Some lichens are very small, so on concrete look for the tiny round, rimmed fruiting discs (ascocarps) of Lecanora and on brick the yellow-green powdery layer of Psilolechia (=Lecidea) lucida, looking like old paint.


About five species of lichen in shades of yellow, grey and brown on a brick wall, Itchen Abbas, Hampshire. Photo © June Chatfield

Ecology
While some lichens specialise in using rock or wood as their substrata, others restrict themselves to acidic or alkaline bark or stone. The relationship between rock chemistry and lichen species is best studied in a churchyard or old cemetery with a variety of rocks from acid granites and sandstones to alkaline limestones and marbles. The texture of the rock surface also affects colonisation by lichens since spores and soredia lodge more easily on rougher surfaces. Streaks of new lichen growth can often be seen below a branch fork or down the vertical face of a gravestone where reproductive bodies are transported by rain runnels. While identification skills are important and a key to further information, opportunities exist for the study of the ecology of lichens, the factors controlling where they live and how they function in their changing world.


Cladonia sp. Cup lichens on heathland Matley Bog in the New Forest. Photo © June Chatfield


Cladonia floerkeana. Photo © June Chatfield

Further reading and reference sources
Lichens by Oliver Gilbert. New Naturalist Series 86, Collins 2000.ISBN 0 00 220081 3 (Hardback), 0 00 220082 1 (Paperback). A readable, well illustrated text, framed around habitats.

Lichens: An Illustrated Guide to the British and Irish Species. By Frank S Dobson. Richmond Publishing, 4th revised colour edition 2000. ISBN 0 85546 093 8 (Hardback), 085546 094 6 (Paperback).

Field Studies Council laminated foldout colour charts. Lichens and Air Pollution (£2.50), Lichens of Rocky Shores (£2.50), Key to Lichens on Twigs (£3.50). Obtainable by post or web from Field Studies Council (Publications), Preston Montford, Montford Bridge, Shrewsbury SY4 1HW Tel: 01743 852140 Email:fsc.publications@ukonline.co.uk Web site : www.field-studies-council.org. Also some book shops in museums.

Lichen Identifier by Frank Dobson. CD Rom. Obtainable from the author. Mr F Dobson, 57 Acacia Grove, New Malden, Surrey KT3 3BU at £27.50. There are many colour illustrations from Photographs.

The British Lichen Society, The Secretary, The Natural History Museum, Cromwell Road, London SW7 5BD or The British Lichen Society website at: http://www.argonet.couk/users/jmgray/

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