An agaric is a type of mushroom which belongs to the genus Agaricus. This mushroom genus has more than three hundred members, some of which are edible, and some of which are poisonous. Many of the most common cultivated edible mushrooms are members of the Agaricus genus.
All agaric mushrooms share several characteristics in common. One of these is the presence of a pileus, or cap, which tops the mushroom in a similar fashion to the canopy of an umbrella. On the underside of the pileus are fine, feathery gills which extend from the center of the pileus to the outer edge. Two other characteristics of mushrooms in the Agaricus genus are the presence of a stem, and of a veil-like structure which protects the underside of the pileus as the fungus develops.
The best known of the edible Agaric mushrooms is Agaricus bisporus, which is known under many different names, and is cultivated in some seventy countries worldwide. Young mushrooms of this variety are typically referred to as a button, white, common, or table mushroom. As the mushroom grows, its flesh darkens, and the cap begins to flatten out. At this stage they may be referred to as baby portobello, Italian, crimini, or brown mushrooms. The mature mushroom, with darker brown flesh and a large, flat cap, is called a portobello or portobella.
Most deaths from mushroom poisoning are due to ingestion of one of two members of the Agaricus genus: either Agaricus phalloides, or an agaric mushroom known as the destroying angel. There are actually several mushrooms which go by this name, all of which are in the Agaricus genus. The destroying angel mushrooms are white, sometimes with a pink, tan, or yellow tinged cap. Deaths due to this fungus usually occur because they are easily mistaken for edible wild mushrooms.
Agaricus phalloides is known as the death cap, and as with the destroying angel mushroom, this fungus appears similar to many edible wild mushroom species. The death cap is one of the most toxic mushrooms known, with an estimated 30 grams, or one ounce, enough to kill an adult human. Contributing to the toxicity of this agaric mushroom species is the fact that symptoms may not appear for two or three days after ingestion, by which time the toxin has already severely damaged the liver and other internal organs.
Many toxic mushroom species are native to multiple countries, and every continent in the world is home to at least one poisonous member of the Agaricus genus, in addition to wild edible mushrooms. Because edible and poisonous members of this mushroom genus are physically similar, it can be difficult for a novice hunter of wild mushrooms to safely gather fungus. Generally it is recommended that a newcomer to this pastime hunt for wild mushrooms under the guidance of someone who has experience in gathering wild fungi.