Coconut Milkcap

The Coconut Milkcap is a small, softly coloured fungus of damp birch woodland, its cap a muted greyish lilac to pinkish grey that blends into the moss and litter it grows through. Size and colour alone would leave it among a crowd of unremarkable little milkcaps; the scent resolves it instantly.

It sits in the group of small dry-capped Lactarius species with scanty unchanging white latex and pale spore deposits. Its finely felted, almost scurfy cap surface distinguishes it texturally from the smooth or viscid grey milkcaps that share its birch habitat.

As an obligate birch associate it is a familiar species across northern woodland, heath and bog margin, and one of the few fungi that can be identified reliably by nose from a metre away in a good fruiting season.

Cap

Small, 2–5 cm across, convex then flattening, often with a shallow central depression and a small low umbo. The surface is dry and matt with a fine felty, scurfy or minutely granular texture, and is coloured pale greyish lilac, pinkish grey or greyish buff, fading paler with age. The margin is thin, incurved at first and sometimes faintly grooved when wet.

Gills

Decurrent to broadly adnate, crowded and narrow, pale buff-ochre with a distinct pinkish or flesh tint, contrasting with the greyer cap. They darken slightly with age.

Stipe

Slender and fragile, 2–5 cm tall and 4–10 mm thick, cylindrical or tapering downward, smooth, coloured pale greyish buff or a shade lighter than the cap, soon becoming hollow.

Flesh and latex

The flesh is whitish to pale buff, thin and very brittle. Latex is white, scanty and unchanging, without a strong staining reaction. The odour is powerful and unmistakable — strongly of dried coconut — and becomes even more pronounced as the fruitbody dries. Spore deposit pale cream.

This milkcap is closely tied to birch, growing on damp acidic soils in birch woodland, birch scrub, heathland with scattered birch, and the wetter margins of bogs. It also occurs occasionally with alder and, rarely, in mixed woodland with other broadleaf hosts. Fruitbodies push up through moss carpets, grass tussocks and leaf litter.

The season runs from late summer through autumn, often in scattered troops of many fruitbodies. It is common and widespread across northern and central Europe, Scandinavia and northern Asia, and occurs in comparable birch habitats in northern North America.

The Coconut Milkcap is ectomycorrhizal with birch, forming a sheath around the host's fine roots and extending a hyphal network into the surrounding peat and litter. Birch is a pioneer tree of poor, acidic and disturbed ground, and its mycorrhizal partners including this species are essential to its nutrient supply on such soils.

The volatile compound responsible for the coconut odour is produced in the fruitbody tissue and concentrates as moisture is lost, which is why dried material smells strongest. Fruitbodies are short-lived and fragile, collapsing within days and feeding litter organisms, while the mycelium persists in the root zone through the year.

Lactarius mammosus shares the coconut odour but is larger, distinctly darker grey-brown, has a more pronounced umbo and grows with conifers rather than birch. The Grey Milkcap (Lactarius vietus) shares birch habitat but has a smooth, greasy to viscid grey-lilac cap and latex that dries grey-green on the gills.

The Birch Milkcap (Lactarius tabidus) is warm orange-brown rather than grey and its latex yellows slowly. Small grey Mycena species may resemble it in colour but are far thinner-fleshed and produce no latex at all.