A long time ago, a strange spore never seen before drifted into the forest. It landed on the ground and got buried under a collection of leaves. A spore is a tiny cell that can produce a new organism. Although the forest community — all the different organisms that live within the forest — didn’t know it at the time, this spore would become a fungus.
Now fungi have been around ever so long. They first appeared on land some 440 million years ago. Plants began to flower only some 120 million years ago. Birds came even later, a mere 60 million years ago. So the fungus’s ancestors were around long before the ancestors of most of the plants and animals in the forest. But the plants and animals had never seen such a spore before. They assumed it was something new.
Once safely nestled under the leaves, the spore grew into a long string of cells. These cells look like a strand of thread and are called a hypha. Hyphae (the plural of hypha) are the building blocks of fungi (the plural of fungus). All fungi with more than one cell are made of hyphae. As time went by, the threadlike cells multiplied in their new damp home under the leaves. They began to weave in and out of each other. Soon they formed a tangled mat that scientists call a mycelium. The new mycelium lived a quiet, underground life. It adapted well to its damp, dark surroundings. Most of the forest community didn’t see it.
There came a moment when the mycelium wanted to reproduce itself. When conditions were right — when there was plenty of moisture — the underground hyphae began to grow upward. No longer did they bunch together in any old tangled way as they did in the mycelium. Now the hyphae wove together more tightly. They produced a stalk, and the stalk rose above the ground. For the first time in its life, the fungus saw light and the forest community. It saw giant, green leaves. It saw bright, red flowers. It saw towering brown trunks. For the first time it felt sad it was merely a humble fungus. It no longer felt like reproducing itself. How could a threadlike mat and a pale stalk compete with the spectacular organisms of the forest?
A passing ant noticed the fungus stalk. The fungus told its problems to the ant. The ant repeated the story to a lizard, who in turn told a bird. The bird woke an owl sleeping in one of the tallest trees and told him. "Tell the fungus not to worry," said the owl. "Soon it will wear a cap and be very proud to be what it is."
The bird told the lizard what the owl said. The lizard told the ant, and the ant told the fungus. But the fungus only sighed.
One day, the fungus noticed something growing on top of its stalk. The thing grew and grew until it formed a large and perfectly rounded cap. No other organism in the forest had such a distinctive cap. Finally, the fungus felt good about itself.
"The owl has given you a cap!" shouted the ant in glee. You see, the ant was somewhat innocent. He didn’t know the owl had no power to make a cap. The owl was merely wise. He had visited other forests. He knew a thing or two about fungi.
Meanwhile, the stalk and the cap together formed what is known as a fruiting body. This is the part of the fungus that produces new offspring. The fruiting body is also called a mushroom. The mushroom is the part of the fungus that most of the forest community sees. From that day forward, the organisms in the forest have called a fungus with a fruiting body a mushroom — not a mycelium or some other such name.
When it examined its new cap more closely, the now-content fungus noticed narrow ridges called gills lining the underside of the cap. Thousands of tiny reproductive cells formed on the gills. These cells united and divided and became spores. The spores left the cap, drifted into other parts of the forest, and started their own mycelium mats. The life cycle of the mushroom began again. Today, hundreds of types of mushrooms and millions of mycelium mats exist in the forest.
And that is how the mushroom got its cap.
Mycorrhiza: Harmful or Helpful?
Some fungi have joined forces with certain plants to make sure they get enough to eat. The term for a long-term association between a fungus and a plant is called mycorrhiza. The hyphae of the fungus grow between the roots of the plant. The fungus helps move phosphorus and other minerals from the soil to the roots of the plants. The plant in turn supplies carbohydrates to the fungus. Scientists call this win-win situation mutualism. It is an example of ways in which fungi interact with the environment around them.