When I built my little water feature a few years ago, I specifically chose a few rocks with lichens growing on them. I didn't know if the lichens would survive outside their native habitat, but I liked the look of them on the rocks.
The lichens are doing just fine. Most likely, their home rock came from nearby and they're adapted to the climate here. Lichens tend to grow on surfaces that are unsuitable for other vegetation. In fact, when conditions are unfavorable to growth and food production, their metabolism shuts down.
Lichens provide food to numerous animals, mostly in the winter. Large ungulates like deer, elk, caribou and others nibble on lichen when other forage is scarce. Squirrels eat lichens and also use them for insulating their nests. Hummingbirds are partial to lichens for their delicate nests as well. Some insects are known to use bits of lichen for camouflage.
Lichens can be put in three categories depending on the surface they choose as home:
1. Epiphytic lichens grow on the bark of trees and shrubs, living or dead. These lichens can take on many shapes and colors.
2. Saxicolous lichens grow on rocks (and, in more recent times, on concrete). They tend to be flat against their host, and colors usually range in grays, browns and blacks.
3. Terrestrial lichens grow on soil. Their shapes and colors can look like either epiphytic or saxicolous lichens. This type of lichen helps prevent soil erosion.
Microbiotic soils are made up of lichens, cyanobacteria and mosses.
A lichen is a partnership between a fungus and an algae. Sometimes cyanobacteria are also part of the partnership.
We're all familiar with fungi. The most well known is the mushroom. Mushrooms don't have chlorophyll and can't create their own food. They grow in decomposing vegetable matter which provides their needed nutrients.
Cyanobacteria, also known as blue green algae, photosynthesize and also fix nitrogen in the soil. Marine cyanobacteria are responsible for about half the photosynthesis of the open ocean.
Algae is green and feeds itself through photosynthesis. For fungi to grow without decomposing material, they team up with algae or cyanobacteria (and sometimes both) in order to get food. The partnership creates a completely different organism called a lichen. According to some researchers, lichens are organisms that have discovered agriculture!
Lichens have no scientific names. When you see a lichen referred to by a scientific name, the name refers to the type of fungus that is the "farmer" of the group. But it's the algae part of the partnership that determines lichen color, shape and where the partnership calls home.
The fungus partner of lichens reproduces with spores. The spores germinate, then have to find their own algae partner or they'll die (and most do die). Some enterprising fungi steal algae from other lichens. Like many other plants, bits broken off from the mother lichen can start another colony, too.
Lichens absorb air pollution and are, therefore, bio-indicators of the health of our air. Pollutants can be measured in their tissue. Lichens are very slow growing and the exact growth rate of some types are known. Those types can be used to determine the rates of pollution at various times.
Lichens have other uses, too. Some are poisonous, some are antibacterial (and used in deodorants). They're used as paints, dyes, in cosmetics and as decorations! A door wreath always looks nice with some colorful lichens attached.
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