Everybody will have encountered at least one species of the wonderful organism explored here. Whether intentionally or accidentally, this organism has caught ones eye and sparked curiosity as to what those mini-shrubs, colourful two-dimensional patches, hair-like strings or gelatinous structures might be. Adorning the bark of trees, stumps or rocks or even the statues in a busy city, it doesn’t just add a sort of natural patina to our surroundings, this inconspicuous organism stems from a much older aeon. With the oldest accepted fossil from the early Devonian 419 – 411 million years ago, lichen has perfected its existence and proven its superiority in the constant battle for essential nutrients.
The first account of this astounding organism dates back to around 300 BCE. Although being the name giver of lichen, Greek naturalist Theophrastus defined a range of algae, mosses and some lichen as such. In the 18th century a Scottish botanist, Robert Morison, attempted to systematically account about 100 species of lichens. In a posthumously published book he skilfully illustrated his identified species. Pier Antoni Micheli and Johan Jakob Dillenius each accumulated detailed classifications of around 300 species in the 18th century. At this point, botanists created classifications at each’ own discretion using the scientific knowledge and trends of the time creating a downright scientific jumble of classifications and naming possibilities. Carl Linnaeus put an end to this in 1753 by standardising the system of naming species and hence laying the foundation of modern scientific nomenclature. 67 of the 80 names in the genus lichen used by Carl Linnaeus are still in use today. Despite his forward thinking, he did not encourage the use of a microscope in his studies, although being available since the 15th century. His student, Eric Acharius, however eagerly introduced the use of a microscope and successfully progressed in the study of lichenology, illustrating spores.
The historic precariousness is understandable knowing what science knows now. The centuries long conundrum and following difficulty in classifying this marvellous organism of lichens is due to its cellular structure. It is a symbiosis of two (sometimes more) organisms in one, making it tricky to classify without any thorough scientific investigation using modern equipment. The bulk of a lichen is a fungus within which tiny photobionts are embedded, typically algae and/or cyanobacteria. While the fungus, the mycobiont, gives structure to the lichen organism, it also protects the algal cells from UV rays and drying out, providing water and minerals. The photobionts of lichen, the algae or cyanobacteria, through photosynthesis provides the fungus with sugar as a source of energy. Fungi are heterotrophs, which means that they retrieve their food from somewhere else. Algae are almost always autotrophs; they make their own food, usually deriving it from sunlight through the process of photosynthesis. Taking into account, alongside environmental circumstances, these inherent characteristics of each component of lichen, the symbiosis offers an obvious benefit over a separate existence. A symbiosis proven to be successful since millions of years.
Lichen appear all over the world. There are, however, recurring themes of environmental factors that favour lichen-domination. Cold places like tundra, high mountain tops, arctic fellfields or Antarctic deserts harbour an abundance of lichen and lichen biomass. Lichens dominate in places where water, in form of fog or dew, can be extracted from the atmosphere, but the soil is too shallow for other plants. Their desiccation tolerance gives them a significant advantage over plants and mosses.
They can completely dry out and then rehydrate and continue as if nothing happened.
Even in other environments, like forests and grasslands where other species of plants and trees are predominant, lichens still appear, not as the prevailing species but in great variety. It’s the various substrates lichens are after; soil, rock, bark and dead wood, and leaves. Each substrate has its own chemistry, and each lichen is after a different substrate, creating almost infinite combinations and microsites. The pH of a substrate determines whether a species of lichen will settle for it or not. Specific species of lichen will appear on surfaces with a high pH, e.g. on limestone, others on substrates with a low pH, like that of granite. Hence, you can find some lichens in human environments.
Lichen doesn’t just take what it needs from its substrate and the atmosphere, it is also a generous provider of water. On a habitat scale lichen biomass can hold thousands of litres of water which it slowly releases to the environment, gravely contributing to the nitrogen cycle.
Lichen is also a source of food for many animals and insects, especially in areas with scarce vegetation.
To a true lichenologist, these marvellous organisms can reveal information about the underlying bedrock, the climate, humidity and air quality, as well as reveal popular canine pee spots and bird perches of the area it is growing in.
Perhaps your next nature walk will be brightened by your own discoveries of the manifold lichens in your environment.
An Article by Rebecca Spangl