Ugly Milkcap Identification Guide

The setting and the first impression

The Ugly Milkcap is a birch fungus, and the search image is a dark blot in wet moss. You are typically in a damp birch stand on acid soil, or on the peaty edge of a heath, a mossy track through a plantation, or a boggy woodland fringe where sphagnum, polytrichum moss and bilberry grow between the trunks. Look for a broad, dull, olive-brown to blackish-green disc pressed into the moss, often half-buried and dusted with fallen birch leaves. It is one of the least colourful large mushrooms you can find, and its whole appearance is muddy and heavy rather than crisp.

Fruit bodies come singly, in scattered groups or in arcs and rings following the drip line of a birch. They are substantial: a mature cap can be 8 to 20 cm across, thick-fleshed and heavy for its size, and they sit low, with a short stem, so that the cap often rests almost on the moss.

Working through the cap

Start with shape. Young caps are convex with a strongly inrolled margin; they flatten and then become centrally depressed, and finally funnel-shaped in age, with the margin lifting and often becoming wavy.

Colour is the diagnostic beginning. The cap is a dirty dark olive, olive-brown or blackish-green, usually darkest in the centre and slightly paler toward the edge, sometimes with a narrow zone of yellowish-olive just inside the rim. In wet weather the surface is distinctly sticky to greasy, and leaves and moss fragments stick to it; in dry weather it goes matt and can look almost black.

Now feel the margin. In young and middle-aged specimens the outer band of the cap, a centimetre or so wide, is finely woolly, downy or shaggy, a soft tomentum that is clearly different in texture from the smooth sticky centre. That woolly rim on an olive cap is one of the most reliable pointers in the field. It wears away in old specimens, so check several fruit bodies of different ages.

If you carry potassium hydroxide solution for chemical spot tests, a drop on the cap surface produces a striking violet to purple reaction, which is a fast and unambiguous confirmation for this species.

Gills, stipe and base

Turn the cap over. The gills are crowded, narrow, and decurrent, running a short way down the stem. In fresh young material they are whitish to pale cream, sometimes with a faint pinkish or straw tint, and they contrast sharply with the dark cap. They stain readily: brush them, cut them or press them and they discolour to dull brown, olive-brown or grey-brown, so that an older or handled specimen shows a blotched, dirty gill face. There are frequent short gills interspersed between the full-length ones, and the gills fork occasionally near the stem.

The stem is short and stout in proportion to the cap, typically 3 to 8 cm long and 1.5 to 3 cm thick, sometimes tapering toward the base. Its colour echoes a paler version of the cap, olive-buff to dirty ochre or olive-brown, and it is slightly sticky when wet. Examine it with a lens for shallow, slightly sunken, darker patches, called scrobicules, which are often present but never as deep or as regular as in some other members of the genus. The stem is firm at first and becomes hollow with age. There is no ring and no volva; the base sits directly in moss and litter, bound with soil and fine roots.

Flesh and latex

This is the step that establishes the genus. Cut across a gill or slice the cap flesh with a sharp blade and watch. Lactarius species exude latex, and in this species it is copious in fresh, damp material. The latex is white and it stays white; set a drop on a clean fingernail or on a white handkerchief and watch it for several minutes. It does not turn yellow, lilac, violet or orange on its own.

What it does do is stain the surrounding tissue. Latex on gill or flesh dries to leave grey-brown to olive-brown discolouration, which is why so many field specimens look dirty and blotched. The flesh itself is firm, white to pale cream, and slowly browns on exposure. The texture is granular and brittle rather than fibrous: the stem snaps like chalk instead of tearing into strings, because the flesh contains spherical cells rather than long fibres. That brittleness is shared with Russula and is a useful genus-level check.

Old, waterlogged specimens produce far less latex, so always test the freshest fruit body available.

Spore print and microscopy

Cut the cap free and lay it gills-down on white paper, cover it to still the air, and leave it two to six hours. The print is pale, ranging from cream to pale buff with a faint yellowish or pinkish cast, and it needs to be viewed on white paper in good light to judge, as thin deposits look almost colourless.

Under the microscope the spores are broadly ellipsoid, around 6.5 to 8 by 5 to 6.5 micrometres, and decorated with ridges and warts forming an incomplete network. That ornamentation stains blue-black in iodine reagents, confirming that a pale-printing, latex-producing, brittle-fleshed mushroom belongs here.

Substrate, season and ecology

Lactarius turpis is ectomycorrhizal and its overwhelming partner is birch. It also associates with spruce in parts of its range, and mixed birch-spruce ground is prime habitat. It prefers acid, damp, often peaty or sandy soils and is very much a fungus of mossy ground rather than bare litter. In much of northern and central Europe it is common wherever birch grows on poor soil, and it has followed planted birches into parts of North America and elsewhere.

Fruiting runs from late summer into late autumn, continuing until the first hard frosts. Because the fruit bodies are thick-fleshed and slow to decay, old blackened specimens persist for weeks and remain identifiable from their woolly margin and decurrent gills.

Separating it from the closest look-alikes

Lactarius blennius is the beech equivalent and shares a sticky cap and white latex. It differs in being paler and greyer, olive-grey to grey-green rather than blackish-olive, in bearing conspicuous concentric rings of darker spots or blotches on the cap, in having a smooth rather than woolly margin, and in growing with beech instead of birch. Its latex dries grey rather than brown.

Lactarius trivialis grows in the same damp northern woods but has a smoother, more lilac-grey to violet-brown cap without the strong olive cast and without a woolly margin, and it is generally a taller, longer-stemmed fungus.

Lactarius pubescens and Lactarius torminosus are also birch associates with woolly margins, but their caps are whitish to pale pink or salmon, not olive, and their marginal wool is much longer and shaggier.

Russula species in the same mossy birch woods can look similar in profile and share the brittle flesh, but they produce no latex whatsoever. A clean cut into fresh gills with no droplets forming rules the genus out at once.

Paxillus involutus, another birch associate on acid ground, has an inrolled margin and decurrent gills that brown when bruised. Separate it on colour, warm ochre-brown to rusty rather than olive-black, on gills that rub off the cap flesh as a soft sheet, on the absence of latex, and on a brown spore print.