Lichens: a partnership between kingdoms
Lichens can be easily confused with plants, mosses, fungi, or bacteria but in fact they are none of these. Lichens are a symbiotic partnership between very distinct life forms - a fungus (and sometimes more than one!) and a green alga and / or cyanobacterium.
The intimate partnerships that are formed have made lichens extremely versatile and allowed them to adapt and thrive across the globe, often in the harshest of environments. There are over 18,000 species of lichen described. Indeed, it has been suggested that up to 30% of all fungi might be able to form lichen associations!
Lichen symbiosis is thought to be a mutualistic relationship, where both the fungi involved (the mycobionts) and their photosynthetic partners (the photobionts) benefit. The mycobionts provide a protective structure and absorb nutrients needed by their partners, while the photobiont converts sunlight into energy that allows the lichen to capture carbon from the atmosphere and make into sugars. These sugars are then used for growth by both partners. This extraordinary collaboration results in the creation of an entirely new organism, the lichen, with characteristics distinct from its individual components.
As lichens, both symbionts can colonise and survive in challenging environments, from the arctic to the blistering deserts, where neither the fungi nor the algae could inhabit alone. In Arctic regions, lichens are essential for soil formation and make up as much as 95% of a reindeer’s diet! In deserts, they can withstand extreme droughts and serve as soil stabilisers, preventing the desert from expanding.
Their remarkable ability to survive in extreme environments, similar to those found on other planets, makes lichens ideal model organisms from astrobiological research. Studying lichens can help scientists understand the potential for life in outer space. Lichens have been used in experiments simulating Mars-like conditions, and their resistance to radiation and desiccation provides valuable insights into the limits of life’s existence beyond Earth. Lichens have even been taken into space to see how they survive - they are truly amazing.
Here on Earth, lichens have found practical applications in traditional medicine. Some lichens possess antimicrobial properties and have been used to treat wounds and infections. Additionally, with a nutritional value similar to that of cereals (!), certain lichen species have been consumed as food, providing essential nutrients and minerals. But unlike cereals, lichens cannot be farmed; they can only be wild harvested. When this is done unsustainably, it poses the risk of extinction for sought-after species. It is also crucial to note that not all lichens are safe for consumption, as some contain toxic compounds.
So next time you are looking at the bark of a tree or staring at the mosaic of coloured patterns on a tiled roof, take a time to think a little bit more about the truly amazing partnerships that can form between fungi and other kingdoms of life.