Mushroom Biology Explained: What Mushrooms Really Are

Mushrooms aren't plants. They're not even close. They're fungi, which means they're in their own separate kingdom of life, completely distinct from plants and animals. And here's the strange part: genetically, mushrooms are actually closer to you than they are to a head of broccoli.

Let’s take a moment to understand why this is important.

When you look at a mushroom, what you're seeing is just the fruiting body. Think of it like an apple hanging from a tree. The apple isn't the tree. It's just the part that produces seeds and disperses them.

The actual organism is underground (or inside a log, or woven through a bale of straw). It's called mycelium, and it's a network of thread-like structures called hyphae that spread through whatever substrate the mushroom is growing on. This network can be massive. The mycelium does all the real work: breaking down organic matter, absorbing nutrients, growing, surviving.

The mushroom you pick or buy? That's just the reproductive structure. It appears when conditions are right (temperature, humidity, light, fresh air), releases spores, and then it's done. The mycelium keeps living, waiting for the next opportunity to fruit.

This is why mushrooms can appear overnight. They're not growing from nothing. The organism was already there, having built up over days, weeks, or months. The mushroom itself is just the final expression.

Plants make their own food through photosynthesis. They take sunlight, water, and carbon dioxide and turn them into sugars. Mushrooms can't do that. They have to consume organic matter to survive, just like animals do.

Their cell walls are made of chitin, the same material that makes up insect exoskeletons and shrimp shells. Not cellulose like plants.

They breathe in oxygen and exhale carbon dioxide. Like you.

They store energy as glycogen, like your muscles do.

This isn't just biological trivia to put in your back pocket. It changes how you think about interacting with mushrooms.

When you're growing mushrooms at home or on a farm, you're not planting seeds in soil and waiting for them to sprout. You're introducing mycelium to a substrate it can colonize and consume.

The mycelium spreads through the substrate (grain, sawdust, straw, whatever), breaking it down and absorbing nutrients. Once the substrate is fully colonized and environmental conditions trigger fruiting, the mushrooms appear.

This is why:

Some mushrooms form partnerships with trees, their mycelium intertwined with tree roots in a symbiotic relationship. The mycelium gets sugars from the tree. The tree gets nutrients and water from the mycelium. Morels, chanterelles, porcini, truffles all work this way. These are mycorrhizal fungi.

You can't easily replicate that relationship in a grow room. The mycelium and the tree are dependent on each other in ways we still don't fully understand. This is why mushrooms like truffles and morels are worth so much money. If you want them, you generally have to go find them in the forest.

Other mushrooms are decomposers, or saprotrophic. Their mycelium breaks down dead wood, leaves, and organic matter. Oyster mushrooms, shiitake, and lion's mane are prime examples. You can grow these at home because you can provide them with exactly what they need: a substrate to decompose.

Knowing which type of mushroom you're dealing with tells you whether you can cultivate it or whether you're stuck foraging.

Understanding that mushrooms are fruiting bodies of a much larger organism changes how you approach everything:

Mushrooms aren't vegetables. They're not plants. They're fungi. And once you grasp what that means, everything else about growing, foraging, and cooking them starts to fall into place.

I hope you’ve learned something today. What questions do you have about mushrooms? Hit reply and let me know what you'd like to know more about.

—Jeremy