Lichen branches out again as smog lifts

It’s only in recent years that hunting for lichen in London has been at all worth it. By the Sixties, air pollution from coal fires in the capital had become so bad that just one lichen out of 130 remained. It wasn’t a very exciting one: Lecanora dispersa looks like a collection of light grey jam tarts.  

As the sulphur dioxide smog has lifted, lichens — which are ever so sensitive to air quality — have returned to pavements and trees, although our air is still toxic with the nitrogen that streams out of vehicles. Lichens make a wonderful wallpaper of bright yellow, green-blue and grey blodges. When you look closer, those blodges turn out to be intricate little worlds of raised spots, miniature leaves and branches.  

Some hide in plain sight. Take another look at the pavement on your walk today. The chewing gum pressed into the flagstones may not have come from someone’s mouth at all. There is in fact a Chewing Gum lichen, Lecanora muralis, which is a dirty grey crust lichen. Harder to miss is the Sunburst lichen, Xanthoria parietina, given it is bright yellow. It grows on walls and pavements. On trees, you’re still most likely to find pollution-tolerant lichens such as the blue-green Lepraria incana. But if you’re near even a scrap of established woodland, hunt on trunks and branches for bushy lichens like the lovely Oakmoss, Evernia prunastri. Even more dramatic than that is the Old Man’s Beard lichen, Usnea subfloridana, which really does hang from twigs like hair long neglected in a lockdown. Cladonia species have cheeky-looking little cups.  

Lichens are a partnership between a fungus and an algae or cyanobacteria. They cover about seven per cent of the earth’s surface and are often the first things to appear in a new habitat, such as bare rock. The clever partnership between the organisms that make a lichen means it can colonise “extreme environments”, including those created by volcanic eruptions — and London.  

Isabel Hardman is assistant editor of The Spectator and author of  The Natural Health Service