Reindeer love it and your trees may wear it, but what is lichen?
Lichen is primitive and complex, but it is not a plant. Nor is it a fungi. Well, not exactly.
Lichens are one of Earth’s more bizarre life forms. You know it when you see it, but that’s usually as far as it goes. Before we learn the secrets of lichens, let’s review some basic plant and fungi facts that will help us understand lichens better.
Plants and fungi
Some 500 million years ago, when life was sorting itself out here on planet Earth, tiny bacteria, called cyanobacteria, learned how to absorb the sun’s light energy and convert it into food. These talented bacteria were swallowed up by primitive plant cells and later evolved into chloroplasts. Chloroplasts are the organelles within plants where photosynthesis occurs.
Fungi - Fungi are not plants. They are their own kingdom and they do not have chloroplasts, which means that they cannot produce chlorophyll or perform photosynthesis. Fungi get all their nutrients from decomposing organic material.
Algae - Algae are also not plants. And they, too, have their own kingdom (Protista). Algae (or alga, if you only have one) come in many different colors. Algae contain chlorophyl but they do not have leaves, roots, true stems, or vascular tissue.
Bacteria - Bacteria are one-celled microorganisms that lack a nucleus. [Did you know that a single teaspoon of soil can contain up to one billion bacteria?] Most bacteria are parasitic decomposers. Many are beneficial. In fact, we could’t digest our food without the help of bacteria in our gut.
Lichens - Lichens are not plants and they do not have roots, stems, or leaves. If you cut a lichen in half, you will often see distinct layers. It’s what makes up these layers that make lichens so strange.
What are lichens?
Lichens are actually two separate organisms living in a symbiotic relationship. A lichen is a fungi combined with either algae or those cyanobacteria mentioned earlier. The fungi is the boss and it dictates the way a lichen functions and grows. The algae and the cyanobacteria perform photosynthesis, providing the combined unit with food. This means that the lichens on your tree are generally not causing any harm. Heavy lichen growths can interfere with light and gas exchanges. Lichens retain moisture and can survive complete dehydration.
Parts of a lichen
While not obvious to the naked eye, lichens have distinct parts:
Types of lichen
There are several different types of lichen, based on their growth behavior:
Lichens reproduce both vegetatively and sexually. Vegetative reproduction can be as simple as breaking off a piece of an existing lichen. All of its natural processes will continue. Bacteria reproduce through cell division (mitosis). The fungal portion of lichen can produce fruiting bodies that release spores which take to the wind and land elsewhere. These spores must mature and connect with suitable bacteria to become a lichen. Since there are several different types of fungi that can become a lichen, the individual structures may vary.
Approximately one-fourth of all fungi are tied up in this sort of arrangement. These fungi are referred to as lichenized. Because of this conjoined arrangement, algae is able to exist all around the world, converting carbon dioxide into the oxygen we breathe. Lichens are also able to absorb pollutants and heavy metals from the atmosphere. You can learn more at the United States Forest Service National Lichens & Air Quality Database and Clearinghouse.
What sort of lichens are growing in your garden?
You can grow a surprising amount of food in your own yard. Ask me how!
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