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Lichen: Reproduction & Life Cycle

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

Living in harmony for thousands of years? This is just one of the neat things that the two organisms that make up lichens have accomplished. This lesson explores these organisms, including their reproductive tactics and life cycles.

Lichen Defined

You're walking in the woods when you stumble upon a grey, mossy-looking object attached to a tree. Puzzled by this mysterious organism, you stop, scratch your head, and contemplate what in the world you're looking at. Is it a plant? A fungus? An alien?

Lichen on a tree
lichen on a tree

This strange mossy clump is a lichen. It is formed from algae and fungi in a symbiotic relationship, or when two species live together and are dependent upon one another. There are lots of goofy ways to remember this. For example, he was a FUN-GUY (fungi), so it's no wonder A-GAL (alga) took a LIKEN (lichen) to him. Also, remember:

  • Fungi is plural
  • Fungus is singular
  • Algae is plural
  • Alga is singular

In most cases, the fungi and algae work as a team; the fungus provides support and access to nutrients and water, whereas the alga provides the food (more on all of that later).

But that's hardly what makes lichen fascinating. Humans have used them for centuries as clothing, toothpaste, and even as deodorant. Lichen can also grow on everything from trees to rocks to soils. There are around 20,000 different combinations of algae and fungi, and six percent of the earth is covered by lichen!

Lichen can grow almost anywhere, including rocks.
lichen on rock

Now that you know a little about lichen, you probably want to here all about their reproduction.

Reproduction

So, how do you think that lichen clump on the tree makes more lichen clumps? Lichen can reproduce using asexual reproduction, where the offspring are genetically identical to a parent, or sexual reproduction, where genetic material from two parents is combined to form a genetically unique offspring. Let's explore each in more detail.

Asexual Reproduction

In many cases, lichen just keep expanding and taking over a region. In other cases, pieces will break off. This is called fragmentation. These pieces can get carried away from the parent lichen via wind, animals, or water.

Another tactic involves soredia, which are made up of algae surrounded, or enveloped, with some fungi. These little bundles break off, get carried away, and then grow in a new location.

An artistic representation of soredium. The center is the alga, which is surrounded by fungi.
soredium

Finally, isidia are globular-like structures containing fungi and alga that break off and create new lichen.

I know. These three modes of reproduction don't' sound particularly romantic, but for lichen they work well.

Sexual

Now onto the sexual reproduction tactic. The fungal portion of the lichen can reproduce sexually, but the new fungus that grows must find it an alga partner. As a result, sexual reproduction has less success than asexual reproduction in the lichen world. The fungus produces a spore, which is dispersed by water, animals or wind, and then the spore will germinate and start to grow. The new fungus finds an alga partner by chance.

Life Cycle

Take another look at the lichen clump on the tree. Let's explore its life cycle, beginning with baby lichen. Remember, lichen can be formed through asexual and sexual reproduction, and life began for that tree-lichen when alga and fungi came together and grew. But it took a while for that lichen to reach the size it did. In fact, most species grow at a rate of one to five millimeters per year. To put that into perspective, it would take between one to five years for your lichen to get to a marble-sized width.

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