Common Stump Brittlestem Identification Guide

The First Impression

You are almost always looking at a stump: a beech or oak stump left from a thinning, a cut birch, a mossy log in leaf litter, or ground above a buried root system. Out of it comes a dense tuft, sometimes an outright crowd, of slender pale-stemmed fungi with brown, dome-shaped caps leaning into one another. Twenty or thirty in a clump is unremarkable, and a large stump can carry several clumps.

Two things register immediately. First, the caps are strikingly two-toned: a dark, water-soaked, date-brown or reddish-brown zone in the centre or around the margin, fading to a pale buff or tan elsewhere, with the boundary between them irregular and blurred like a tidemark. Second, the whole assemblage looks fragile. The stems are thin, white, and shining, and the caps sit lightly on them. Nudge the clump and pieces break rather than bend.

This is a late-summer to late-autumn fungus, and one that reappears in the same place for years while a stump lasts.

Reading the Cap

Size and shape. Caps are roughly 2 to 6 cm across. They start almost hemispherical or bluntly conical with a strongly inrolled edge, then broaden to convex and finally to nearly flat, usually keeping a low broad hump at the centre.

Hygrophanous behaviour. This is the key cap character. The flesh is thin and holds water, so colour tracks moisture directly. A saturated cap is a deep date-brown to chestnut or reddish-brown. As it dries, pallor spreads outward from the disc, leaving a pale tan or clay-buff centre with a darker band still lingering at the margin. Watch a collection over an hour on a dry day and you will see the change happen. Blotchy, marbled, half-and-half caps are normal and are a positive character rather than a sign of a poor specimen.

Margin. In young caps the edge is finely striate when moist, the lines showing the gills beneath. More importantly, it carries white veil remnants: small pale fibrillose teeth, flecks or a fine fringe hanging from the rim. These are delicate and are shed early, so examine the youngest caps in the tuft.

Surface. Smooth, matte to slightly greasy when wet, never scaly and never truly viscid.

Reading the Gills

Attachment. Adnate, meeting the stipe squarely, sometimes with a very slight notch.

Spacing. Crowded and narrow, with intermediate tiers.

Colour sequence. Pale greyish-buff or clay when young, then dull brown, then a dark grey-brown with a distinctly purplish or violaceous cast at maturity. Hold a cap at an angle against the light to see the purple undertone, which is the genus signature.

Edges. With a lens the gill edges are usually finely whitish and slightly uneven, contrasting with the darker faces, and on humid days small clear droplets bead along them and dry as dark spots.

The Stipe, Base and Flesh

Stipe. 4 to 8 cm long, only 3 to 6 mm thick, cylindrical, straight or curved where crowding forces it. White to very pale cream, often with a silky, slightly shining, finely fibrillose surface, and frequently a faint dusting of pale fibrils near the apex where the veil once attached.

Hollowness and the snap test. The stipe is hollow, or at least stuffed and quickly hollowing. Take one between finger and thumb and bend it. It does not flex: it snaps cleanly and audibly, like a dry piece of chalk or a matchstick, leaving a clean break rather than a fibrous tear. That brittleness is the single most useful tactile character in the group and is why they are called brittlestems.

Ring. None. At most an evanescent fibrillose zone.

Base. The stipes of a tuft converge but do not fuse into a single stout common base. The lowest part is often clothed in white downy mycelium binding wood fibres, and if the tuft appears to arise from soil, dig a little and you will find buried wood.

Flesh. Very thin, watery pale brown in the cap when moist, whitish when dry, and pallid in the stipe. Cut a fruitbody lengthwise and watch: there is no colour change of any kind on the cut surfaces, and bruising produces at most a dull brownish smudge.

Taking and Reading the Spore Print

Because so many wood-tufting fungi resemble one another, the print is the deciding evidence.

Choose a mature cap that has flattened out and whose gills have gone dark. Cut the stipe off flush, lay the cap gill-side down on white paper, and cover it. These caps are thin and dry fast, so keeping humidity in under a bowl matters more here than with fleshier species. Two to three hours is usually enough.

The deposit should be a heavy, dark purplish-brown to blackish-brown, reading almost chocolate with a purple cast when thick and clearly violaceous when smeared thinly with a fingertip. A rusty or foxy orange-brown deposit rules the species out entirely.

Under the microscope the spores are small, smooth, ellipsoid, roughly 4.5 to 6 by 3 to 4 micrometres, dark brown in solution, with an inconspicuous germ pore. Their small size relative to other dark-spored wood dwellers is a helpful check.

Substrate and Season

The species is a decomposer of dead broadleaf wood: stumps, fallen trunks, large branches lying in litter, sawn timber left in the wood, and buried roots. Beech and oak are classic hosts, and birch, ash, poplar and willow all serve. Conifer records exist but are much less usual.

Fruiting runs from late summer through autumn and often into early winter in mild conditions. The characteristic habit is dense caespitose tufting: many fruitbodies rising from a shared patch of colonised wood, elbowing one another so caps become distorted. Repeat flushes from the same stump across several seasons are normal, and the species is widespread throughout temperate Europe, North America and Asia.

Separating the Look-Alikes on Morphology Alone

Pale Brittlestem (Psathyrella candolleana) shares the brittle white stipe and dark print but its cap is far paler, whitish-cream to honey or pale tan even when moist, and it never shows the dark date-brown saturated stage. Its veil remnants are larger and more conspicuously toothed, its gills pass through a distinctly lilac phase, and it usually grows in smaller groups from buried wood at path edges and in grass.

Clustered Brittlestem (Psathyrella multipedata) grows in very dense bundles whose stipes fuse into a single narrow common base emerging from soil, and its caps are smaller, paler and more conical.

Sulphur Tuft (Hypholoma fasciculare) has yellow to greenish-yellow caps, gills passing through sulphur yellow to olive-green, and tough flexible stipes that bend instead of snapping. The print is purple-brown in both, so use gill colour and the snap test.

Conifer Tuft (Hypholoma capnoides) likewise has a tougher stipe, a tawny-ochre cap without the strong hygrophanous tidemark, grey gills, and conifer wood beneath it.

Sheathed Woodtuft (Kuehneromyces mutabilis) also has a two-toned hygrophanous cap, which makes it the trickiest visual match, but it carries a definite membranous ring with small recurved scales on the stipe beneath, and its spore print is a bright rusty brown.

Glistening Inkcap (Coprinellus micaceus) grows in similar tufts on stumps, but its young caps are tawny-ochre under a coating of glistening mica-like veil granules, its caps are strongly grooved, its gills deliquesce into black liquid, and its print is black.