About this fungus
Cucumber Cap is a fungus in the Macrocystidiaceae family. Its habitat and field characteristics are summarised below.
A small red-brown to date-brown mushroom with a paler cap margin and a slender velvety stem that darkens towards the base. Its strong cucumber, fish oil or rancid-oil odour is unusually distinctive.
What to check
Check the dry finely velvety cap and stem, blackish stem base, pale gills that become pinkish or yellow-brown, pink-brown spore print, absent veil and strong cucumber-like or fish-oil odour. Smell is supportive, but microscopy of the unusually large cystidia may be needed for confirmation.
Variation
Moist young caps can be very dark brown or almost black, with a contrasting pale edge. Drying and age produce lighter reddish-brown or buff tones. The odour varies in intensity and is sometimes perceived as cucumber, herring or rancid oil.
Lookalikes
Pluteus species have free pink-maturing gills and usually grow directly from wood, but lack the same velvety blackening stem and characteristic odour. Flammulina species grow on wood and have white spores. Other small brown mushrooms require a spore print and microscopic checks rather than smell alone.
Habitat and range
Saprotrophic on humus-rich soil, leaf and needle litter, garden beds and woodchip mulch, sometimes in large groups. It is widespread across Europe and North America and is also recorded as an introduced fungus in Australia.
Food safety
Inedible.
Photographs
Tim Sage / CC BY-SA 3.0