A mushroom is a fungus that fruits anarchically in nature. A fungus is a spore-producing organism. As opposed to seeds, spores are cells that can reproduce without combining with an other spore.
Mushrooms are ranged into many varieties and species: some mushrooms have stems, some other not. Some have a bowl-shaped cap, some have a flat cap. The size of mushroom's caps vary widely, and their color as well.

Identifying mushrooms is not an easy task, it demands to regard the mushroom as an assemble of microscopic spores. Mycologists know how to proceed: they take a look at below the mushroom's cap and draw their conclusion from the cap's gills.
The standard mushroom, illustrated in many books, is the combination of a white stem with a withe-spotted red cap. But many funny species exist, with a different morphology: the stinkhorn is a penis-like mushroom, the puffball is a little brown ball that “goes up in smoke” when you crash it...

Usually we tend to classify mushrooms into 2 categories: the toxic mushrooms and the edible mushrooms. Edible mushrooms are used in many cuisine! The best valued mushroom is the truffle: for 2,5 pounds of truffles, a Honk Kong buyer paid 112 00000$ at an auction!
Toxic mushrooms are poisoning and eating them may be lethal. Their chemical substances may alter the mind, and sometimes make them glow in the dark...

The most “funny” but dangerous type of mushrooms are the psychoactive or “magic” mushrooms. These are psychedelic drugs, which like LSD produce hallucinations, increased senses (visual acuity...)... In Alice in Wonderland, a children book, Alice takes a chunk of the Caterpillar's mushroom, a side of which would make her grow taller, the other smaller...
In Mario video games, mushrooms also seem to contain a psychoactive element: mushrooms are power-ups that make Mario grow taller and stronger. Toad, a Mario's character, is the recurrent mushroom character, chief of the Mushroom Kingdom!