(Mycena species)
There are over 100 species of bonnet in the UK and many cannot be accurately distinguished without expert microscopic examination. For most of us non-experts, it's maybe enough to identify that we have found a Mycena species rather than another similar small fungus.
Features of all Mycena are a fragile stem and a cap that starts almost conical, progressing to bell/bonnet shape, and flattening as it ages. If you'd like to take a spore print, they all have white spores, so take a cap and leave spore-side down it on black/dark paper.
All Mycena are small, from tiny pin sized to a few cm.
Bonnets can be found most of the year, but less so in spring. They're saprotrophic (they feed on dead organic matter including wood and leaves), so play an important role in woodland nutrient cycling.
The Common Bonnet is often found in clusters on well rotten, moss covered stumps and logs.
One of the Mycena species that is slightly easier to identify is the Lilac Bonnet (Mycena pura). Shown here when ages into a flattened disc shaped cap, the cap is 2-5cm and often pink or purple in colour, fading to white around the margins which are quite distinctly lined, especially when wet. Despite it's common name, the colour of the Lilac Bonnet can be quite variable, sometimes grey to white, making it less distinct. They're bioluminescent, emitting a weak green light. This very common fungus is toxic.
Bonnet fungi are introduced in 'The Tree That Held The Moon' to inspire curiosity in the wonders of nature.