Meeting Mycorrhizae

A partnership you can't see

Imagine you could shrink down small enough to walk among the roots of a tree. You would find something surprising: the roots are not alone. Wrapped around them, and sometimes even reaching inside them, are the fine threads of a fungus.

This close partnership between a fungus and a plant root has a name: mycorrhiza (say it "my-koh-RYE-zuh"). The word comes from Greek: mykes means fungus and rhiza means root. So mycorrhiza literally means "fungus-root." When we talk about more than one, we say mycorrhizae.

Meet the threads

Most of a fungus is not the mushroom you spot on the forest floor. The main body of a fungus is a web of tiny threads called hyphae (say "HY-fee"). Each thread is far thinner than one of your hairs. Together, thousands of them form a tangle called a mycelium.

In a mycorrhiza, these fungal threads team up with a plant's roots. Some fungi form a soft sheath, like a sock, around the outside of the root tips. Others send their threads right in between the plant's own root cells. Either way, the fungus and the root end up living pressed together, sharing the same tiny patch of soil.

Not a rare trick

You might think such a close friendship would be unusual. It is the opposite. Scientists estimate that more than 80 out of every 100 kinds of land plant grow with mycorrhizal fungi. Oak trees do it. Pine trees do it. Grasses, wildflowers, and many crops in a farmer's field do it too.

In fact, mycorrhizae are so common that a plant growing without a fungal partner is the exception, not the rule. This partnership is one of the oldest on land. Fossils show plants and fungi were already teaming up hundreds of millions of years ago, when the first plants were spreading across bare ground.

Why it's called a symbiosis

When two different living things live closely together, biologists call it a symbiosis. Some symbioses help only one partner. But the mycorrhiza is special because both partners gain something, which makes it a mutualism — a partnership where everyone wins. Exactly what each side gives and gets is the puzzle we will unwrap in the next lesson.

Safety note: The mushrooms and fungal threads in a forest are fascinating to study, but never pick or taste a wild mushroom. Some are harmful, and only a trained expert can tell them apart. Look closely, ask questions, and leave them where they grow.

You have just met one of nature's most important teams. Next, let's find out what they trade.