Last Thursday we visited Felbrigg Hall, a National Trust property in North Norfolk. We took the train from Norwich to Roughton Road and walked through the grounds of the estate. On the way home we headed back to Cromer on the Weaver’s Way footpath and caught the train home.

Larger fungi were noticeably scarce and in low numbers in the woods after a punishingly hot and dry summer that dried the soil out so thoroughly that recent rains are only starting to re-wet it.

But in the grass outside Felbrigg Hall one species of fungus was abundant. The lawn was covered in masses of Brownedge Bonnets, Mycena olivaceomarginata.

Mycena olivaceomarginata grows gregariously among grass and mosses in meadows, unfertilized lawns and open grassland, including dunes and dry coastal slopes. In Norfolk I find it in churchyards after rain in September and October and I’ve found it on the grass path on my allotment in the past two years. This year it has also turned up on our lawn and on Saturday I saw it in Eaton Park in Norwich and on some of the grass verges in neighbouring streets. As we walked back to Cromer on Thursday there were masses of Brownedge Bonnets in the field which Weaver’s Way crosses on the way down  to Cromer Hall.

Mycena olivaceomarginata is a saprotrophic fungus, obtaining its nutrition from dead organic matter. As any lawn owner will know, the summer drought killed off a lot of grass leaves and left bare patches in lawns. Brownedge Bonnets are now fruiting in these places, feeding on the grass debris. They are having a year of abundance.

Brownedge Bonnets are quite variable in appearance but they’re always quite small with conical caps 5-20 mm across. These vary in colour from greyish to grey-brown or dark brown, often with a yellowish or olivaceous tint, or with a pinkish or reddish shade at the centre. They have a slight nitrous or radish-like smell (note 2).

The Brownedge Bonnet’s specific name, olivaceomarginata, means “with olive margins”. The edges of the gills are yellowish brown, pink-violet or reddish brown, though this coloration can be quite subtle and not especially easy to photograph, but I’ve made an attempt in the picture below (note 1).

Distribution of Mycena olivaceomarginata

There are lots of records for Mycena olivaceomarginata in East Anglia and in many parts of southern England and I expect there to be many more this year, if the situation in Norfolk is repeated across the country. Brownedge Bonnets can also be found in Wales, Scotland and Ireland.

Further afield, Mycena olivaceomarginata has been found in much of Europe, parts of North America and Asia and in New Zealand. There is a worldwide distribution map on the Global Biodiversity Information Facility (GBIF) website.

Other bonnets are available

There are many other bonnets. Worldwide, the genus Mycena contains about 500 species and there are over 100 species  in Northern Europe alone, many of them in Britain. They vary in size from larger species like the Lilac Bonnet, Mycena pura (cap diameter 15 – 50 mm, stem 40 – 90 mm long by 2 – 7mm wide) to much smaller species such as the Frosty Bonnet, Mycena tenerrima (cap diameter 2 – 5 mm, stem 5 – 30 cm long but only 0.2 – 0.3mm wide).

Habitat is often a useful clue. Mycena olivaceomarginata grows in grass but others such as Common Bonnet, Mycena galericulata, grow on dead wood. Clustered Bonnet (Mycena inclinata) grows mainly on dead oak wood. Some of the smaller species grow on tree bark or moss on tree trunks. One, Mycena belliae (Reed Bonnet) grows on dying reed stems just above the water level.

Microscopy is often necessary to identify bonnets to species, looking at structures such as cheilocystidia (cells projecting from the edges of the gills) and spores.

Luckily not all bonnets are hard to identify and several have novelty features such as bleeding coloured juice. They’re always among the highlights of a fungal foray.

The Burgundydrop Bonnet, Mycena haematopus, exudes purplish red juice like red wine when damaged. Americans give it the less poetic name of “Bleeding Fairy Helmet”.

Saffrondrop Bonnet, Mycena crocata, is even better. It bleeds bright orange-red juice when the cap or stem is damaged.

Further Reading

General fungi field guides all feature some of the commoner species of bonnet but you may soon encounter species that you can’t identify.

As the next step, Geoffrey Kibby’s “Mushrooms and Toadstools of Britain and Europe, Volume 2” features a good range of the British species (£38).

The complete and indispensable guide book is “The genus Mycena s.l.” by Arne Aronsen and Thomas Laessoe (Volume 5 of “Fungi of Northern Europe”). It costs £64, so is probably only for the more serious (or rich) mycologist.

The website Mycenas of Northern Europe is very good too and complements the Aronsen and Laessoe book.

Notes

Note 1 – The Yellowedge Bonnet, Mycena citrinomarginata, is much yellower than the Brownedge Bonnet, with yellow to yellow-green gill edges. It can be found in lawns but is also found under trees and usually grows on woodier debris than Mycena olivaceomarginata. It is comparatively scarce in Norfolk with just nine records to the end of 2025. In contrast, there are 106 records for Mycena olivaceomarginata.

Note 2 – According to Wikipedia the mycelium of Mycena olivaceomarginata is bioluminescent. See the Wikipedia page “list of bioluminescent fungi“.