Lichens are strange organisms, with some plant-like features, but which are actually a partnership of an alga or cyanobacterium that makes a home for fungi, which feed their partner with nutrients. They are also a warning sign of the changing climate. Mediterranean species are increasing in the UK as the climate grows warmer with longer dry spells, while species that enjoy cooler weather are disappearing. Lichens are often highly sensitive to air quality, and decades ago many vanished from towns and cities that were polluted with coal smoke. When the smoke was banished, lichens returned in the cleaner air, but now urban lichens are under attack from traffic pollution. And in the countryside, they suffer from ammonia air pollution due to farming with fertilisers and animal slurry.
And yet lichens are so rugged they are found in some of the most hostile areas on Earth, from the freezing cold, dry valleys of Antarctica to searing hot deserts, and they can be completely dried up and still come back to life when rehydrated. Lichens have even survived in space – one study kept lichens on the outside of a satellite and the International Space Station and they withstood intense ultraviolet radiation, low temperatures and no water. In fact, lichens would be ideal for a mission to colonise Mars.
