Macrocystidia cucumis

Cucumber Cap

Fungus of the month - November 2010

(old scientific names include Agaricus cucumis, Naucoria cucumis and Nolanea pisciodora)

This is a ‘small brown job’ but actually quite distinct once you get your eye in for it. The cap can grow up to 5cm across and usually has a rich, dark red brown rather velvety appearance. The colour will fade as the cap dries out. The cap can be conical or more flattened with either a broad or papillate umbo. The edge of the cap can be faintly striate and is often a paler and contrasting yellow brown colour. The gills are paler, starting out white and becoming a reddish ochre colour; they are adnexed. The stipe is stiff, pale at the apex, but dark and velvety below.

The spore print is a pale pinkish buff colour (described as brown in some books) and yet the genus is placed in the Tricholomataceae (usually white spored) by many authors. Others place it in Entolomataceae (pink spored). It is the smell that really gives the game away – it ranges from putty, through cucumber to distinctly fishy – along the lines of cod liver oil. This fact is underlined by the specific names in past and current taxonomy.

The combination of habitat, macro characters and the distinct smell make this almost always identifiable in the field and then easily confirmed with a microscope. The sterile cells on the edge of the gill (cheilocystidia) are relatively enormous looking like a palisade of spear blades!

The Cucumber Cap is a saprotrophic or ‘recycler’ fungus, which is breaking down dead plant material. Fungi are the only group of organisms that can break down lignin and without them we would be buried under many metres of woody debris. They also lay a vital role in driving the carbon cycle, releasing nutrients that they don’t require back into the habitat.

Fruiting: occurs throughout the year but can also be found in the late autumn and winter months

Habitat: on rich humus or nitrogen rich soils thus often in nettle patches and increasingly on woodchip mulches in gardens and parks

Distribution: (Checklist of the British and Irish Basidiomycota Legon & Henrici 2005): Scotland (England / Wales / NI) – occasional – or at least infrequently reported.

The total number of records for this species on the Fungal Records Database of Britain and Ireland is 660 with 60 of those originating in Scotland.

As with so many fungi, this species is almost certainly overlooked – possibly because it often occurs late in the season when people are less often out foraying.

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