The wonderful world of lichens

Get up close to the forest floor, the trunk of a tree, or even a manmade wall or sidewalk, and you will see: Lichens are everywhere. Glowing in bright colors or dazzling with their impression of minature forests, lichens aren't just beautiful - they are also scientifically fascinating.

Lichens grow where few other species stand a chance. Appearing to describe the contours of some alien land, this Rhizocarpon geographicum - or map lichen - gets on just fine on a bare rock in Norway.

Lichens are made up of fungus and algae that thrive in a symbiotic relationship. The fungus (colored brown here) deposits the algae cells (green) in its mycelium. Through photosynthesis, the algae produces sugar from carbon dioxide and water - and feeds its fungal host.

You might recognize this Scandinavian reindeer lichen (Cladonia stellaris) from floral arrangements, or model railways where it's painted to represent tiny trees and bushes. In its natural habitat, reindeer rely on this lichen as a staple of their winter diet.

Not all lichens make for such a nutritious meal. This vividly colored wolf lichen (Letharia vulpina) is one of the few poisonous members of the species. In days gone by, it was stuffed into animal carcasses to poison wolves and foxes.

Lichens are very sensitive to pollutants in the air - some so much so that they can be found in very few places on the planet. These gigantic beard lichens (Usnea longissima) festooning the branches in a Norwegian forest used to be found in Germany too - but the species is now extinct there.

Despite their sensitivity, lichens can also be wonders of extreme survival, thriving in deserts and mountaintops - and even Antarctica. This plucky little specimen has even made a home for itself on a discarded plastic bottle in the Galápagos.

The intricate folds of this leaf-like organism give it the name Iceland moss - a name that will be familiar to some from teas and tablets to sooth sore throats. In fact, this traditional remedy isn't a moss at all, rather a lichen.

From a lichen that looks like foliage to a lichen that looks like … a rock perhaps? Or bark? Leucodecton occultum, or volanco lichen, grows in the Galápagos and is among the more strikingly unusual species.

Lichens reproduce via fungal spores. This descriptively named brown beret lichen (Baeomyces rufus), found in Europe, North America and Asia, produces little fruiting heads to release it spores.

Scientists estimate there are more than 20,000 species of lichen. And they keep discovering new ones. Despite its dramatic coloring, this Lepidostroma rugaramae in Rwanda was only recently described. Who knows what they will uncover next? Author: Brigitte Osterath