Liken’ the Lichen: Naturalist Notes
When I was a young child I loved to climb trees. What child doesn’t? I remember sitting up in my favorite tree and seeing this gray-green thing growing on it. One of my siblings told me it was something that would kill the tree. So, I spent days scraping off as much gray-green flaky stuff as possible, thinking I was helping.
Fast forward a few, or rather, many years, and I learned what that “stuff” actually was. Lichen! Lichen is a symbiotic partnership between two or more organisms, all from separate kingdoms. Fungi, algae, and/or cyanobacteria all come together in a complex life form.
Lichen on a tree.
Fungi is not a plant as it does not produce its own food, so it grows wherever it can get nutrients from other organisms. Algae and cyanobacteria are both capable of producing their own food through photosynthesis, but they are limited to very watery habitats. Lichens, being a combination of at least a fungi and alga, can go where no alga has gone before. The fungus can protect its algae so these normally water-requiring organisms can live in dry, sunny climates. On the flip side, twenty percent of the world’s fungal species would not be able to grow in nature if it weren’t for lichenized fungi. What it means is that you will never find that species of fungus out in nature without being in lichen.
Lichens do not have any roots, stems, or leaves, so they have creative ways of getting what they need to survive. Their outer layer, or the cortex, is composed of fungal cells that help with protection. Just beneath the cortex, there are algal and/or cyanobacterial cells that contain chloroplasts that produce the food. Lichens are capable of absorbing water vapor from the atmosphere. You can tell what kind of algae a lichen has based on the color. When a lichen is dry, its color is usually gray and it goes dormant, essentially turning off. When a lichen is wet, it turns back on, and the cortex cells become transparent while the algal cells underneath get to show off their color. This is when photosynthesis and growth happen. See the embedded image below.
On the left is lichen on a maple tree, the second is that same lichen after getting it wet. You can see the color change after just a few seconds.
In some lichens, the different organisms are not in separate layers, but in a gelatinous mixture called jelly lichens.
There are three main growth forms of lichen; foliose, fruticose, and crustose. Foliose lichens have two easily distinguishable sides, a top side and a bottom side. These lichens can be very flat, leafy (like lettuce), or full of ridges and bumps. Fruticose lichens can be pendant and hair-like, upright and shrubby, or upright and cup-like. Crustose lichens are just that, crusts. They form a crust over a surface (like a rock).
Lichens do not have a straightforward way to grow more lichen. Can you imagine how two different species living in the same body reproduce? The fungi are the dominant partner in the relationship and get to develop spores. These spores produce another fungus, but if it does not find another algae partner it will die. Lichens have adapted to their bi-species struggle and can reproduce vegetatively. This means fragments can grow into full-size lichen.
Lichen is not only captivating, but it can also be quite useful. Humans use lichens as food, medicine, clothing, poison, deodorant, decoration, and dye. From the original Christmas tree tinsel to the purple robes of the wealthy, lichen was there! Many indigenous people would turn to lichen as a food source in harsh times. However, some valued certain species of lichen as a staple of their diets. Disclaimer, not all lichen is edible, and in fact, some are poisonous.
The most prominent use for lichen is as a natural dye. Historically, purple was one of the hardest dyes to make and therefore coveted by royals. One article I read talked about how mixing certain lichen with ammonia became the primary source of purple dye. Where did they get the ammonia you ask? Peasants would sell their urine.
Animals use lichen too! They provide food, shelter, and building materials for elk, deer, birds, and insects. Some insects cover their bodies with lichen to camouflage! Hummingbirds will cover the outside of their nest with lichen for camouflage and insulation.
There are over 14,000 species of lichen worldwide and over 600 here in Michigan. If you want to go lichen hunting our local hotspot is Isle Royale. Now you don’t have to go to Lake Superior to find lichen, you can find it on any rock or tree in your own neighborhood. I encourage you on your next walk to look for lichen, and when you find it, pour some water on it to see the color change! Also, next time you come to the nature center for a visit, look at some lichen under the microEYE!
Submitted by Cathy Wesley, Naturalist, August 2022