Porcelain FungusBeing an amateur naturalist I have often come across this issue of what is the difference between a mushroom and a toadstool. And the answer is simple - there is no difference because neither is a 'correct' scientific term.
The fungi comprise a large group of organisms that includes microorganisms such as yeasts and moulds, as well as the more familiar mushrooms/toadstools. Fungi are classified as a kingdom that is separate from plants, animals and bacteria. One major difference is that fungal cells have cell walls that contain chitin, unlike the cell walls of plants, which contain cellulose. These and other differences show that the fungi form a single group of related organisms, named the Eumycota (true fungi or Eumycetes), that share a common ancestor (a monophyletic group).
Mucilago crustacea - a slime mould
This fungal group is distinct from the structurally similar slime moulds (myxomycetes) and water moulds (oomycetes). The discipline of biology devoted to the study of fungi is known as mycology, which is often regarded as a branch of botany, even though genetic studies have shown that fungi are more closely related to animals than to plants.
The terms mushroom and toadstool are both used to apply to the fleshy body of any of numerous fungi - both edible and inedible.
an Agrocybe species
To complicate matters the term mushroom is sometimes used to include toadstools and sometimes they are used the other way round. How can something include something else that has the same meaning? The answer lies in whether the fungal fruiting body has a stem and a cap with gills. If it does it may be described as a mushroom (or toadstool) to differentiate it from some fungi that don't have these three features.
A Boletus species - with a stem and cap but no gills!
A further way in which the terms are confusingly used is that 'mushrooms' is sometimes used for edible species and 'toadstools' for poisonous ones. Since some edible species look identical to poisonous ones and can only be told apart by microscopic examination of the spores this is the most unhelpful (and potentially dangerous) of the ways in which the names are used.
This Yellow Stainer is poisonous and yet it looks
like the sort of 'mushrooms' you buy in the shops.
In summary, therefore, they are all fungi and the terms mushroom and toadstool are usually used loosely to refer to fruiting bopdies with caps, gills and a stem.
(If you enjoyed this post thank Dawn Treader for the idea. If you got bored or confused half way through, blame me!!).