Lichen offer food and shelter to a wide variety of organisms, they are excellent at measuring air quality and ecological value, and they are beautiful to look at. But not many of us know what they are, or how to differentiate one from the other.
Learn more about the incredible world off lichens with our identification guide.
Lichens are not plants, but bizarre, barely understood mixed organisms in a mutual co-operation: half fungus, half alga, and sometimes home to cyanobacteria too. The alga or bacterium produces simple sugars from photosynthesis and the fungus creates a structural matrix, the thallus, in which to house its powerhouse ‘guest’. The thallus absorbs water from the atmosphere so lichens can grow on extreme, virtually water-free substrates, such as bare rock, tree trunks, brick and stone walls. They can also survive severe desiccation by becoming metabolically inactive. Learn more about lichen with Richard Jones’ guide to eight of the most common.
Eight lichens to look out for in the UK
Gold lichen, Caloplaca flavescens
The same colour as painted yellow lines, it fades to orange or lemon with elongated radiating lobes. Grows in rounded encrustations to 10cm across, with a central area resembling crazy paving. Apothecia (fruit body) are darker orange, 1.5mm across. Found everywhere on walls, exposed limestone and gravestones.
White lichen, Diploicia canescens
Pale grey to brilliant white, rounded or irregular-oval encrustation to 6cm with long overlapping lobes at the margins. The centre breaks out in powdery pale greenish white floury soralia (reproductive structures), 1–5mm. Found on trees, walls and rocks in lowland England and Wales, coastal Scotland and scattered in Ireland.
Map lichen, Rhizocarpon geographicum
Strong yellow-to-pale-green encrusted rosette, up to 15cm in diameter, with a distinctive crackled appearance and small (1–3mm across) black apothecia scattered all over. An upland species, usually found on exposed hard granite and silica rock, it’s common in Scotland, Wales and the West Country, more scattered in England and Ireland.
Oak moss, Evernia prunastri
Thallus-forming, bushy, branching, strap-like tufts of pale greenish-grey clusters with miniature antlers hanging down. The underside is paler, sometimes almost white. It grows on the bark of broad-leaved trees, and is particularly obvious on twigs and small stems, giving a mossy appearance. Found throughout the British Isles.
Black-spot lichen, Physcia aipolia
Black-spot is pale green or bluish grey with a loosely folded and encrusting rosette up to 6cm across. Spotted liberally with grey-dusted blackberry-jam-tart apothecia, 2–3cm in diameter. It grows on tree trunks, branches, logs and stumps throughout the British Isles.
Handwriting lichen, Graphis scripta
Large, pale-green or cream encrustations. It is smooth, but etched all over with small, regularly spaced black hieroglyph-like marks (slit apothecia) that are wrinkled, curved and often branching. Under a lens, the margins seem to be raised, lip-like. Found on tree bark, especially in partial shade, throughout the British Isles.
Cup lichen, Cladonia fimbriata
The cup lichen has an irregular, overlapping, pale-green leaf-like thallus forming dense mats from which trumpet-shaped fruiting bodies (30–40mm high) erupt. It is found growing on the ground and on tree roots and logs throughout the British Isles. One of the most commonly collected lichens.
Leaf lichen, Peltigera membranacea
Large, folded, pale grey-brown body of thin but broad leaf-shaped bracts forming large clusters to 40cm across. The undersides are ribbed with branching vein-like ridges. Its fruiting trumpets with grey stalks are tipped bright orange like damp matches. Widespread across the British Isles, especially in the west and north.