The Encyclopedia of Toadstools is a book found at Flourish and Blotts. When players visit the store in Chapter 4, Moment 3 of Chamber of Secrets, this is one of the books that's flying around. It is about to hit Lucius Malfoy in the eye. The book can be collected.
From the Story
"This book hits Lucius Malfoy in the eye during the struggle with Arthur Weasley in Flourish and Blotts."
"Everything you ever wanted to know about toadstools."
- On Pottermore the book is called Encyclopedia of Toadstools. However, the file name for the book's image has the alternative spelling Encyclopaedia of Toadstools.