Mushrooms are a group of fungi that make up an entire biological kingdom unto themselves. With many different genera and species, mushrooms all have the ability to absorb food through their cells from their surrounding environment. Some mushrooms form beneficial or parasitic relationships with other plants, using them as a food source, while others feed on and break down dead organic materials. Many are edible, including white mushrooms (Agaricus bisporus), but some are toxic and poisonous; however, all mushrooms have similar but varying descriptive characteristics.
Mushrooms spring up from under the soil via a stalk, or stem, which acts as a support structure. Commonly, mushroom stems are vertical with a straight, cylindrical or tapering shape. Mushroom stems may be thick or thin, and some may bulge at the base. The stem may appear fleshy or flattened and has a variety of textures, from rough to smooth or scaly. Depending on the genera and species, mushrooms may have lateral stems. There are even some varieties that have no stems at all. Mushrooms have a thin ring around the upper portion of the stem and another ring toward the base of the stem, also called the volva.
Sitting on top of the mushroom's stem is the most distinctive feature in identifying mushrooms: the cap. The cap is typically a convex umbrellalike top positioned over the stalk. However, some genera and species produce caps that are flattened or nearly concave. During immature stages, the cap of the mushroom hides the stem; resembling an egg, this stage is also referred to as the button stage. Mushroom caps continue to change and evolve as the fungus matures. They come in all different colors and textures, from brown to white to vibrant colors such as red or pink. Mushroom caps may be scaly, rubbery or smooth. They also range in moisture, from dry to wet or greasy in appearance.
If you turn a mushroom over or remove the cap and observe the underside, you'll see an array of ribbedlike structures called gills. Like the cap, these gills also come in many colors, which may match or contrast with the color of the cap. Some mushrooms have more gills than others, and the spaces between them can be wide or very narrow. Mushroom gills are also attached to the stem differently depending on the genera. Some do not connect directly with the stem, while others curve upward or downward, attaching at the stem.
If you cut a mushroom open, the inner flesh is usually meaty or rubbery, but it may also be soft or crumble easily, depending on the variety. The color of the flesh also may not match the outer color of the mushroom cap, gills and stem. When exposed to the air, the flesh may begin to change in color over a period of a few minutes to a few hours. Other mushrooms contain liquid within the flesh, excreting a milky substance whenever the mushroom is punctured.
Some unseen features that are unique to mushrooms include the way in which they reproduce. As mushrooms develop into a mature fruiting body, they are capable of releasing billions of spores to begin the cycle of reproduction. When the conditions are hospitable, the spores germinate, creating strands called hyphae. The hyphae take in nutrients to help the mushroom develop. They evolve into an underground mass called mycelium, which in turn produces the fruiting body aboveground, known as a mushroom.