In A Nutshell
The terms “mushroom” and “toadstool” are purely unscientific labels applied to different varieties of fungus. While there’s no real scientific difference or definition, the two terms have come to mean different things in the common parlance. The name “toadstool” is often given to those fungi that are inedible or poisonous, while “mushroom” is generally reserved for those that are safe to eat.
The Whole Bushel
There’s no real, scientifically accepted difference between a mushroom and a toadstool, and the terms can sometimes be used interchangeably to refer to the same types of fungus. However, in common, non-scientific usage, the term “toadstool” is more often given to those fungi that are poisonous or otherwise inedible.
This is by no means a worldwide, written-in-stone distinction, however, and shouldn’t be used to judge whether or not a mushroom is acceptable to eat. One of the most deadly members of the fungus family, the death cap, isn’t referred to as a toadstool, but a mushroom. There are an amazing amount of different varieties of mushrooms and toadstools, but one thing you should not do is use wives’ tales (e.g., “if you can peel it, it’s safe”) as a guide to what’s harmful and what’s not.
Both toadstools and mushrooms can be defined as the fruiting bodies of a fungus—that is, these are the part of the fungi that produce spores. Most of the fungus itself is underground, and the cap appears in the autumn months for most types. The only purpose of the cap is to release the fungi’s spores; the other parts of the fungi, including those that process and draw nutrients from dead and decaying matter, are underground, and we just never see them.
When most people envision a toadstool or a mushroom, they tend to think of a fungi that has a defined stalk and a cap. There are other types of fungi with less traditional forms, such as the puffball, an aptly-named round, white ball fungi with no apparent stalk. These types of rather non-traditionally formed fungi are typically referred to as mushrooms.
So why have toadstools become associated with the less desirable, more deadly type of fungus?
The answer is in the word itself. Toadstools were once believed to be exactly that—places that toads liked to sit. And since toads were also thought to be poisonous or carriers of disease, that quality transferred to the fungi they were said to favor. The term “toadstool” dates back to the 14th century and has also been recorded as “tadstoles.” Toadstools were also rumored to be a food source for the less-than-savory animals, sometimes called “toad’s meat,” “toad’s cap,” or “toad’s cheese.”
The poisonous variety of fungi have had a variety of names over the centuries, including “wart caps” and “Devil’s droppings.” Toads were also closely associated with the Christian devil, who took the form or attributes of a toad in many old European stories from Milton’s Paradise Lost to medieval folk tales, fairy stories, and wives’ tales.
It’s important to note that names like “Devil’s droppings” are completely warranted for some of the nastier types of poisonous fungi. Many cause mild to moderate gastrointestinal distress, but some types of mushrooms can cause internal hemorrhage, kidney or liver failure, and even psychosomatic symptoms like confusion and anxiety after eating. In some cases, symptoms might not set in for hours or even a few days after ingesting the poisonous toadstool—or mushroom—and in some cases a complete recovery may seem inevitable before organ failure or ruptures.