Ugly Milkcap

Lactarius turpis, also published as L. necator and L. plumbeus, is the darkest of the common birch milkcaps. Its cap is a heavy olive-brown to blackish green, often looking grimy because the sticky surface collects soil, moss fragments and needles, and the specific epithet turpis means ugly or unsightly.

Structurally it is a solid, broad-capped species with an inrolled and finely downy margin, crowded pale cream gills that contrast sharply with the dark cap, and copious white latex that stays white but leaves brown stains where it dries on the gill surface. Mature caps flatten and become funnel-shaped, and the olive tones darken further toward black in old or waterlogged material.

One of the most useful supporting characters is a chemical one: a drop of potassium hydroxide on the cap surface or flesh produces an immediate strong violet to purple reaction, unmistakable and instant, which sets it apart from other dark milkcaps.

Cap

The cap is 6–20 cm across, convex with a strongly inrolled margin, becoming flat and then broadly funnel-shaped. It is dark olive-brown, olive-green to almost blackish, usually darker at the centre, and the surface is distinctly sticky to slimy when moist, which is why it is so often coated with adhering debris. The margin is finely downy or minutely fibrillose in young specimens.

Gills

Gills are adnate to shortly decurrent, crowded, narrow, and pale cream to dirty white — a strong contrast with the dark cap. They stain brown to olive-brown where bruised or where latex has dried, so mature specimens often show dark blotches and streaks across the gill face.

Stipe

The stipe is 3–8 cm tall and 1.5–3 cm thick, short and stout, tapering downward, olive-brown to dirty buff and paler than the cap. It is often slightly sticky, sometimes shows shallow pits, and becomes hollow with age. No ring, no volva.

Flesh & spore print

The flesh is whitish, firm and brittle, browning slowly where cut. It releases copious white latex that stays white but dries brownish on gills and flesh. Potassium hydroxide gives an immediate deep violet reaction on cap and flesh. The spore print is cream, with warty, partly netted spores.

Lactarius turpis grows with birch and is one of the most consistent birch associates in northern woodland. It favours damp, acidic ground — mossy birch woods, the edges of bogs and mires, Sphagnum margins, wet heath and boggy woodland tracks — and it also appears on drier acid sand where birch is well established. Occasional records come from spruce in mixed northern forest.

It is common throughout northern and temperate Europe, abundant in Scandinavia and the Baltic region, and extends across northern Asia. It has been introduced with planted birch to parts of North America and Australasia. Fruiting is from late summer through autumn, often in large numbers, and the fruiting bodies are frequently found half-buried in moss.

This species is ectomycorrhizal with birch. The mycelium builds the standard mantle-plus-Hartig-net structure on fine roots and extends an extensive network into moss and peat, capturing nitrogen and phosphorus from substrates where those elements are locked up in slowly decaying organic matter. In Sphagnum-rich birch mires it is often among the dominant fungal partners.

The sticky cap surface traps litter and may reduce water loss, while the copious pressurised latex floods any wound and deters invertebrate grazers. Fruiting bodies are large, persistent and heavily colonised by fungus gnat larvae, and their slow decay returns concentrated nutrients to the moss layer while dispersing spores through the surrounding ground.

Lactarius blennius, the Beech Milkcap, is also slimy but is a much paler grey-green to olive-grey with faint concentric spotting, and it grows with beech rather than birch; its white latex dries grey rather than brown, and it gives no violet reaction with potassium hydroxide. Lactarius fluens is likewise a beech species with a paler olive cap and a distinct pale marginal band.

Lactarius trivialis shares damp birch and conifer ground in the north but has a smoother lilac-grey to dull violet-brown cap without the heavy olive tone and without a downy margin. Lactarius plumbeus is generally treated as the same fungus under a different name rather than as a separate species.