Lichen in Cuyahoga Valley National Park

Lichen is an impressive, yet often overlooked organism. We frequently see it growing on trees, rocks, or mosses. There are many kinds of lichen, with some looking flat and dusty like, and others having leaf-like offshoots. What really is lichen, and what makes it so special?

What is Lichen?

Lichen is a composite organism, meaning that it’s made up of two or more species. Lichen is made from algae or cyanobacteria, and a fungi species. This cyanobacterium (or algae) lives within the filaments of the fungi. These species share in a mutualistic relationship, meaning that they are working together and both are benefitting from the relationship. While some lichens do look similar to moss, they are very different and are not closely related to any kind of plant. However, like many plants, lichens do produce food through photosynthesis. Lichens do not have any roots.

What Makes Lichen Special?

Lichen can grow under extreme conditions. They’re found everywhere from the arctic tundra to deserts and from sea level to alpine elevations. They can be found hanging from branches or growing on rocks, trees, and dirt.  About 6-8% of the earth’s surface is covered by lichens, and there are about 20,000 different kinds. Some reproduce sexually, while others reproduce asexually.

Lichen only grows 1-5mm per year, with some lichen growing even less than 1 mm per year. Some Antarctic lichens are estimated to be 500-5000 years old. Some have even been estimated to be 8600 years old (possibly the world’s oldest living organism). Because of lichen’s unique ability to grow in many diverse conditions and to live long durations, we sometimes use them to date historic events. Lichen can be sensitive to environmental stress such as air pollution, air quality, and metal contamination. As a result, they are often used as bioindicators to measure ecological health and quality.

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