Fungal fundamentals:What is a mushroom made of?

Hyphae, mycelium, and fruiting bodies

 

One of the most important things to learn about mushrooms is that what you’re seeing is just a small part of the organism. The main body of a fungus is almost always hidden away out of sight. When the fungus wants to reproduce, it sends up a mushroom, which disperses spores somehow (usually by dropping them into the air, where they blow away on the wind) and hopefully the spores land somewhere hospitable and start growing into a new fungus.

The main body of a fungus is composed of a mass of what look like fine threads or roots, called hyphae. They are usually just a single cell thick. If the fungus is eating a log, these threads will penetrate throughout the wood, secreting digestive enzymes that dissolve components of the wood that the fungus then absorbs and feeds on.

If the mushroom is symbiotic with trees or other plants, its hyphae interweave with the plant’s roots so they can exchange nutrients and water. Likewise, if the fungus is parasitic on a plant (or animal), its hyphae will penetrate the host organism, again dissolving and feeding.

Sometimes when a mushroom is picked, some of the hyphae that gave rise to it remain attached to it, looking like fuzz or fine roots at the base of the stalk.

When hyphae are several cells thick, rendering them easy to see with the naked eye, they are called rhizomorphs. Rhizomorphs often have a tough rind, and — being thicker than regular hyphae – they are more resistant to drying out. Some fungi send them out to find and colonize new locations. Honey mushrooms are especially fond of this, producing “black shoestring” rhizomorphs in great quantities.

While the individual threads are called hyphae, the collective mass of them, comprising the main body of the fungus, is called the mycelium. Some fungi will produce spores directly on their mycelium, but the fungi we are most interested in here grow a new organ specifically for that purpose. One of the ways that fungi are different from people is that because they’re mostly only one cell thick, they don’t really have an interior. So while people have most of their organs on the inside of their body, fungi generally grow their organs on the outside, and discard them after use. Organs that serve to disperse spores are called fruiting bodies.

Fruiting bodies are made of hyphae also; it’s just that the hyphae are packed very tightly to form, for instance, a solid-feeling cap and stem. Although a cap and stem are the form of a fruiting body that we generally learn first in the West, fungi produce fruiting bodies in a tremendous variety of shapes and sizes, which we will discuss in later posts. Here are a few of them:

Some people reserve the term “mushroom” for a fruiting body that has a cap, stem, and gills. Generally on this site, if we’re talking about a specific kind of fungus and its physical features, we use the term “mushroom”; and we use the term “fruiting body” when we’re talking more about its biological features.

Because of the difference in function between the mycelium and the fruiting body, the main body of the fungus is sometimes called its vegetative portion. This does not mean that the mycelium is sitting around on the sofa, watching TV and eating chips! What it means is that the mycelium is primarily occupied with gradually eating and growing, in a way that reminded early mycologists of plants.

This “vegetative phase” of eating and growing is how the fungus accumulates the biological resources to be able to grow and support the fruiting body. So if you ask a mycologist why you’re not seeing mushrooms on a log, she may say “Well, it’s still busy vegetating,” or “I guess it’ll need to vegetate some more before it can fruit.” Mycologist talk can sound very strange at times, but it makes sense if you know the concepts they’re using.