How do you lichen me now?
Often unnoticed and disregarded, our many exquisitely sculptural and brilliantly coloured lichen species are some of the natural world’s most complicated and clever organisms, observes an admiring
The humble lichen species that coat trees and rocks in many colours are worth a closer look, says an admiring John Wright
GO for a walk along a country lane or city high street—it matters not which—and you will see lichen. From below the high tide of a rocky shore to the tops of high mountains, from just south of the North Pole to just north of the South Pole, lichens are quietly living their lives. Lichens are the most widespread of all complex organisms and yet we pass them by, unnoticed and disregarded, also-rans after the furry, the feathery and the flowery. Yet beautiful they certainly are, with sometimes brilliant colours, and exquisite in both their sculptural detail and functional complexity.
Lichen biology is a mystery to most, but the fundamental facts are simple enough. A lichen is a symbiosis, a mutualism, between a fungus (the structural part) and a ‘photobiont’, which will be either (rarely both) an alga or a cyanobacterium. The photobionts supply both themselves and their fungal partner with the carbohydrates of photosynthesis. When the relationship was first discovered, the photobiont was viewed as a captive slave. However, photobionts fare very well in the relationship, physically supported by the fungus, supplied with trace nutrients and protected from ultraviolet light, grazing animals and desiccation.
The fungus involved is nearly always an ascomycete—a major fungal grouping that also includes morels, cup fungi and yeast, but there are also a few basidiomycete lichens. This grouping includes the familiar bracket fungi and mushrooms, so the reproductive body of a basidiolichen may be small mushrooms instead of the cups and rounded black projections that produce the spores on the ‘asco lichens’.
My first attempt to identify lichens came in about 1965, with The Observer’s Book of Lichens—it’s still on my desk as I write. Handicapped by profound ignorance, the complexity of the subject, the mostly greyscale images and lack of patience, my career as amateur lichenologist ended after a 10minute read. I have done marginally better since, now able to name about 40 species, although identifying all but the most common or distinctive of the 2,000 British lichens is notoriously difficult. Nevertheless, it is well worth learning at least some of those easy species or simply to observe closely that beauty of structure.
Apart from their arcane nature, the trouble with lichen for the novice is simply words. The standard field guide contains a glossary of more than 200 specialist terms; the excessive number due to terms being required for lichens themselves, plus for all three of their component kingdoms. Worse, there are almost no consistent common names, so you will have to get used to such delights as Myxobilimbia epixanthoides. Worse still, lichens as such don’t have Latin names, the name they go by being that of the fungus. Have fun!
String-of-sausage lichen Usnea articulata
Draped from high and low branches, Usnea articulata is a large and graceful species, loose-woven from a multitude of long, palegreen threads. That grace is slightly compromised, however, by the threads near its attachment taking on the form of a string of long sausages, although it does explain ‘articulata’. U. articulata is a common sight in the South-west, yet it is rare to non-existent elsewhere. Usnea species are extremely sensitive to sulphur dioxide and, once they were lost to SO2 pollution in their more eastern locales, they never returned when air quality improved: a fate shared by many other lost species. Not even the countryside is free from such problems, as many lichens are highly sensitive to ammonia and can suffer greatly from the spreading of slurry.
Oak moss lichen Evernia prunastri
During the Bosnian war, the suffering population was reduced to eating wild foods. This very common lichen, found on twigs of deciduous trees, was one of them. I collect it to add an interesting aroma to other foods and for a fragrant smoke for smoked sloe gin. It is difficult to describe the smell, but I always say it smells like Debenhams (I used to, anyway). The department-store comparison is not surprising, as it has long been employed as a fixative in perfumes.
Hammered crottle lichen Parmelia sulcata
This very common species is a pale green, leafy and found on trees, rocks and wooden gates. As with most lichens, it reproduces both sexually and asexually. Parmelia sulcata, however, seems rather coy about the former, so relies on asexual reproduction for the most part, forming soredia (powdery fragments of lichen) from the edges of its fronds. Quite how lichens attach themselves to their substratum may not be a question you ever thought to ask, but I shall tell you anyway. With leafy lichens such as P. sulcata, they are effectively ‘nailed’ in place by wiry, black structures known as ‘rhizines’. I have mentioned technical terms already,
but the material of which rhizines are made is a real star :‘ conglomerated pro so plectenchy ma to ushyphae ’.
Leptogium turgidum (no common name)
We all have a vague idea of what lichens should look like and Leptogium turgidum isn’t it. Instead of forming a generally fruticose (bushy), crustose (crusty) or foliose (leafy) structure (thallus), it consists of small, hollow blobs of dark-brown jelly. You may have seen something like it before on pathways in the form of (unsettling) masses of convoluted brown jelly. This is the cyanobacterium, Nostoc commune, and it is a Nostoc species that is the photobiont in
L. turgidum. There is a great example on top of a sarcophagus outside my village church. It is worth mentioning that churchyards are among the best places to look, because they are disturbed infrequently and lichens on tombstones frequently come with a date.
Heath navel lichen Lichenomphalia umbellifera
There is a little brown, umbrella-shaped mushroom that grows on soil or damp wood that was once called Omphalina ericetorum. It was then discovered that its mycelium (the main part of the fungus that gives rise to the mushroom) does not live on dead organic matter as expected, but on a mass of small, dark-green granules of algae, all connected by mycelium and sitting on the soil surface. It is a basidiolichen. Because there were other Omphalina species that did not live in this way, its generic name was changed. It is not a species I see very often, but a great delight when I do.
Bitter wart lichen Pertusaria amara
I am very fond of species that have distinguishing tricks up their thalli to help with identification. Pertusaria amara can be identified with a glance and a lick. Lichens produce about 1,000 chemicals, generally known as ‘secondary metabolites’, which
means they are used for something other than growth or reproduction. Most of those chemicals have been found only in lichens and they are being carefully screened for use in medicine and elsewhere. (John Wyndham would be thrilled, although his philosopher’s stone has proved elusive.) Precisely what these chemicals are for is mostly a mystery, but many are known to defend against being eaten. Bitter tastes work extremely well— P. amara is truly, horribly bitter and the taste does not wear off for an hour.
Common sunburst lichen Xanthoria parietina
It is quite likely that you will see this species every time you step outside as, due to its high tolerance of pollution, it is common almost everywhere. Still, it is a great beauty, its generic name reflecting its colour, ‘golden yellow’. Unfussy about habitat, it cheerfully grows on trees, rocks, walls and roofs. Entire urban landscapes can be golden from above thanks to this lichen, the roof tiles of a hundred houses hosting the fungus, often fertilised by birds. The reproductive bodies, the apothecia, form pretty golden cups.
Script or secret writing lichen Graphis scripta
With most lichens, up close and personal is the only way to view them. This lichen is most often seen as a grey-beige patch on the trunks of smooth-barked trees. Nothing to see here, then. However, with a loupe (small, high-powered magnifying glass) the details are astonishing. The entire, unprepossessing surface seems to be covered with a scattered Demotic script: vague Js, Ls, Ys, Us and more, dancing around each other. The Latin name means ‘writing writing’ and the black markings are long apothecia that produce and eject the fungal spores.
Spotted felt lichen Sticta canariensis
Although the Latin name means ‘pierced thing from the Canaries’, this lichen nevertheless grows in Britain (albeit rarely). Sticta canariensis is unusual in containing both an alga and a cyanobacterium as photobiont—the one used being dependent on light levels. A colony may employ its cyanobacterium at the bottom of a gully, its alga at the top and both halfway up. In the shaded bottom, the lichen will be branching and blue-green, whereas, at the light and airy top, it will be leafy and green. Halfway, it will be a mixture of the two.
Grey reindeer lichen Cladonia spp.
My earliest encounter with a lichen was with Cladonia portentosa. This bushy species is one I have known since I was a child, when it found perfect use as, well, bushes for my tiny soldiers to hide behind on elaborate papier-mâché battlefields. It is still used in model railway layouts and is rather put upon, as it is collected from its native heathland in devastating quantities. A lichenologist friend tells me of his occasional encounters with collectors gathering sacks of the stuff to sell. Words, it seems, are spoken. A less bushy species, C. polydactyla, is found not on heaths, but on rotting wood. With the use of a loupe, its unremarkable form is revealed to have a treasure in the form of multiple fruiting bodies, which are a brilliant scarlet.