The body of a fungus is usually hidden from view. The main vegetative part is the mycelium, a tangled web of fine, thread-like filaments called hyphae that grow through soil, wood, or other substrates. When conditions are right, the mycelium produces a fruiting body, the spore-bearing reproductive structure that most people recognize as a mushroom. Mushrooms are not the whole organism; they are merely the temporary reproductive tip of a much larger mycelial network. A few fungi also produce hardened survival structures called sclerotia, dense masses of mycelium that can endure harsh conditions and later sprout new growth. The distinction between mushrooms and molds is essentially that mushrooms are visible fruiting bodies while molds are usually just mycelium without obvious fruiting structures.
A typical mushroom has several recognizable parts. The cap, or pileus, holds the spore-producing surface, which may take the form of gills, pores, or teeth on its underside. Gills are thin radiating blades, pores are spongy tubes, and teeth are spine-like projections. The stem, or stipe, supports the cap. Many young mushrooms are wrapped in protective tissues: the partial veil covers the gills or pores and tears as the cap expands, often leaving a ring called an annulus around the stem, while the universal veil encloses the entire button and leaves behind a cup-shaped volva at the base and sometimes warts on the cap.
Reproduction begins when mature mushrooms release microscopic spores through sporulation. Spores drift on wind, water, animals, insects, and even raindrops. A useful identification technique is the spore print, made by setting a cap on paper under a bowl for several hours; the falling spores leave a colored pattern that helps narrow down the species. The fungal lifecycle proceeds from spore germination, through mycelial growth, to the formation of tiny primordia or pins, and finally to mature fruiting bodies that release new spores, a process that can take weeks to years depending on the species. Many fungi can also reproduce asexually by releasing spores or by fragmentation of the mycelium, while yeasts reproduce largely by budding. Some fungi have multiple mating types rather than the familiar two sexes, and sexual reproduction often involves fusing hyphae from compatible partners before producing spores.