Scotch Bonnets, Fairy Ring Champignon (Marasmius oreades)

Phylum: Basidiomycota. Class: Agaricomycetes. Order: Agaricales. Family: Marasmiaceae

Scotch Bonnets are an early season mushroom and get their name from the shape of the cap. It has a little nipple-like bump in the middle and its overall shape looks like piece of headwear that was worn in Scotland a while back. The other common name ‘Fairy Ring Champignon’ comes from the fact that this is the mushroom that makes fairy rings in lawns. ‘Champignon’ means basically ‘edible mushroom’.

They can grow in clusters or in open ended arcs (incomplete circles) as well, so the rings are only a guide to identification, not a fixed characteristic. Fairy rings are, traditionally, where Fairies dance. This dance is invisible to most humans and if you cross the circle while a dance is happening, you will be compelled to join in! So for dignity’s sake, harvest from outside the circle.

Interestingly, the grass close to a Scotch Bonnet is greener than grass that is not so near. This seems to be because of a hormone that the mushroom releases that makes the grass greener. Maybe this is an evolutionary adaptation to lure grazing animals that will then eat the grass and mushroom and distribute the spores that way? Maybe it’s a way to lure Scotsmen?

Scotch Bonnets can dry out completely and spring back to life when water it rains. That is caused by a sugar called trehalose, which prevents severe cell damage when the mushrooms become dried out. As the mushroom cells rehydrate, they consume the trehalose and this helps them return to normal and even start producing spores again! Trehalose also has the benefit of making the mushroom taste sweet taste when cooked. It’s my favourite dried mushroom.

Scotch Bonnets usually occur early in the season. There are a few similar mushrooms that grow in similar conditions so make sure you check the ID guide below.

Identifying Scotch Bonnets (Marasmius oreades) – a summary

If you find a ring or partial ring of small brown mushrooms on your lawn or an oval or park, the likelihood is that they’re Scotch Bonnets but check for these details first –

• Cap is 2 – 5 cm across. Creamy white to tan in colour with a distinctive nipple (called an ‘umbo’) in the middle that is usually darker than the rest of the cap.
• The cap starts off bell shaped, then flattens out as it ages.
• Gills are widely spaced and DO NOT continue down the stem. There is another, inedible, mushroom that grows locally in similar locations which has gills that do.
• The widely spaced gills have smaller gills in between them. The gill colour is cream.
• Smooth, tough stem, up to 5 cm long and solid. Up to 5 mm in diameter.
• Spore colour is white.

For reference, they’re listed on page 123 of ‘A field guide to Australian Fungi’ by Bruce Fuhrer.