HOW DOES LICHEN LOOK LIKE?
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All lichens are unique and present themselves in various shapes and a wonderful range of colors, ranging from blue-grey to orange-red. Furthermore, lichens react to humidity, making them truly dynamic; rehydration can cause some lichens to unfold into a flower-like form, changing their color and making them appear more alive. Lichen can have many growth forms, but traditionally, lichen has three main growth types: crustose, foliose and fruticose.
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Crustose: crust-like lichens
A crustose lichen, as its name suggests, is crust-like and two-dimensional. Some crustose lichens are thick and lumpy, others are thin and smooth, and some are grainy. The crust is close to the substrate and some or almost completely submerged into the substrate with only apothecia emerging to the surface. This also means that they are difficult to remove from the substrate without at least partial destruction of one or the other.
Foliose: flat leaf-like lichens
A foliose lichen has flat leaves with two easily distinguishable sides; a top side and a bottom side. The leaves are somewhat like lettuce, however they can be convoluted and full of bumps and ridges. These lichens have rhizoid-like (root-like) outgrowth to attach to the surface but are generally not firmly bonded to the substrate on which it grows.
Fruticose: miniature shrub-like lichens
Fruticose lichens have a more three-dimensional structure and can be coral-like, bushy, shrubby, hanging or upright, and cup-shaped. However, their main stems are most of the time round in cross-section. Different from crustose and foliose, fruticose lichen is only attached to the base of the substrate.
WHERE CAN I FIND LICHEN?
You can find lichens, in many places, not only in nature but also in the city and even in your garden. Lichens are true pioneers and an very curious life-form that can be found in environments where other plants struggle to exist. They can make hostile places, their home, and even pave the way for plants to take over. Think about places with very little nutrition or surfaces that cannot be penetrated by most plants (stones). Lichen depends on water and light. This means most lichen in Europe, including the Netherlands, grows on the South-west side because it has the biggest source of light and water available.
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The surface where lichen can attach to and grow is called a substrate. There are many suitable substrates for lichen, ranging from tombstones all the way to old bikes. However, lichen can be divided into four substrates they grow on: trees (epiphytic), wood (lignicool), stones (epilitic), ground (territric)
Note:
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Most lichens have a specific preference for one type of substrate
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Many lichens are adapted to tolerate a wide variety of changing environments, while some species are strictly attached to particular habitats.
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LICHEN AS BIO-INDICATORS
An important role in keeping both nature and people healthy
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Because lichens do not have any roots they are not harmful to their physical environment. They simply hold on to the surface, whether it is ground, stone, or tree, and retrieve their nutrients directly from the air, rainwater and light instead. This makes them very sensitive to air pollution, enabling them to respond in a remarkably clear way to environmental changes.
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Each lichen has its own story: one likes acidification, while the other likes nitrogen. Some lichen thrives in a warm climate, while the others enjoy more frigid temperatures. This means that you can notice the changes in a certain environment, by recognizing different lichen species and observing the increase or decrease of lichen over the years. It is worth mentioning that lichens grow very slowly, just a few millimeters each year.
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In other words, lichens uncover a lot about the health of our environment and whether the air we breathe is clean and healthy or not. This is particularly the case in the Netherlands, where in the last twenty years the effects of air pollution with ammonia (NH3) on lichen are clearly visible and mainly caused by manure, but also by traffic and industry.
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Note: Most information about lichen, as well as the specific selection of lichens are inspired by and retrieved from Bryologische en Lichenologische Werkgroep: https://www.blwg.nl/.
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Lichens that thrive because of ammonia
Lichens that dissappear because of ammonia
Other Lichens that are also worth looking for
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