A hypha (pronounced “HY-fuh”) is a single thread-like strand that makes up the body of a fungus. If you've ever seen fuzzy white or gray mold growing on old bread or fruit, you were looking at thousands of hyphae tangled together. Each individual hypha is so thin you can barely see it without a microscope, like an incredibly fine piece of thread.

Hyphae grow by extending at their tips, branching out in search of food. As they spread, they release enzymes that break down whatever they're growing on (bread, leaves, wood, or soil) so the fungus can absorb nutrients. When many hyphae weave together into a visible mass, that network is called a mycelium. The mushrooms you see above ground are just the fruiting bodies; the main body of the fungus lives as a vast network of hyphae underground or inside rotting wood.

The plural of hypha is hyphae (pronounced “HY-fee”). Scientists studying fungi spend lots of time examining hyphae under microscopes because their structure helps identify different species. Some hyphae have walls dividing them into compartments, while others form long tubes without divisions.