Red Edge Brittlestem Identification Guide

First Impression and Setting

Autumn, a shaded path edge, a garden border, a mulched bed or a patch of rough grass over buried woody debris. What you see is a scatter of extremely slender mushrooms standing 6-14 cm tall on stalks no thicker than a matchstick, each carrying a tiny conical cap. They look fragile because they are: brush one and the cap may fall, and a specimen carried loose in a pocket will arrive as fragments. Colour differs from fruit body to fruit body in the same troop - some caps dark date-brown, others pale buff - which is not variation between species but the same species at different stages of drying.

The genus impression is unmistakable once you have met it: thin, brittle, hollow white stalk; small hygrophanous cap with a translucent, lined margin; dark gills. The species character then comes from a hand lens on the gill edge.

Reading the Cap

The cap is small, 1-3 cm across, conical to bell-shaped when young, expanding to convex or almost flat with a low broad umbo. Fresh and moist it is a rich date-brown, reddish-brown or dark tan, and the margin is finely striate - you can see the lines of the gills through the flesh, which is barely a millimetre thick.

Now watch it dry. Hygrophanous caps lose water outward from the centre, and this species does it visibly: within an hour of picking, a pale ochre or greyish-buff zone spreads from the middle to the rim, sometimes leaving a two-tone cap with a dark outer band. Recording the moist colour, not the dried one, is essential when comparing with descriptions. The surface is smooth to very finely wrinkled or corrugated when dry, matt, and sometimes shows a few pale veil fibrils on the extreme margin in young buttons; there is no persistent hanging veil curtain.

The Gills and the Red Edge

Turn the cap over and get the lens on it. The gills are adnate or slightly notched, moderately crowded, and quite broad relative to the small cap. Colour marches through the fruit body's life: whitish to pale greyish in buttons, then clay-grey, then purple-brown, and finally very dark blackish-brown as the spores mature, usually mottled during the transition.

Along the very edge of each gill, in mature but not decayed material, is a fine line of pink, rosy or reddish pigment. It is narrow - a fraction of a millimetre - and it is easiest to see against the dark face of a fully mature gill, in good light, from a slightly oblique angle. Rotate the cap while you look. This coloured edge is the feature the common name refers to and, in combination with the habit and the rooting base, it is the primary field character. Note two practical points: very young fruit bodies whose gills are still pale often show it weakly or not at all, and old, wet or collapsing specimens lose it. Pick middle-aged material.

The Stalk and Base

The stalk is disproportionately long and thin: 5-12 cm or more, only 1-3 mm thick, straight or slightly wavy, white to very pale greyish, silky-shining, hollow, and snapping cleanly rather than bending. Under the lens the upper part is finely pruinose and the lower part often bears scattered white fibrils. There is no ring and no volva.

Excavate the base rather than pulling the mushroom. Two features live down there. First, a small cushion of white mycelium binding soil, litter and woody fragments. Second, and more usefully, the stalk often continues below ground as a narrow tapering rooting extension, a pseudorrhiza, running down towards buried wood. Losing that root by yanking the fruit body throws away a genuine character, so lever the soil away with a knife.

Flesh and Colour Change

The flesh is thin, watery and concolorous with the surface, pale in the stalk and brownish in the cap. There is no colour change on cutting or bruising, no latex, no blueing. The odour is faint and unremarkable. That absence of reactions is itself informative: it steers you away from groups that redden, blacken or exude.

Taking a Spore Print

A print is quick and worth doing. Cut the stalk flush, lay the cap gill-side down on white paper, cover it with a small container to reduce airflow, and leave it two to four hours - the small cap drops a lot of spores quickly. The deposit is dark purple-brown to blackish-brown, and against white paper you can judge the purple tone by scraping the deposit into a dense ridge with a blade.

Under the microscope the spores are smooth, ellipsoid, dark red-brown in water, with an obvious germ pore at the narrow end, roughly 10-14 by 5-7 micrometres. If you can prepare a gill edge mount, the pigmented cells crowded along the edge explain the visible red line and confirm the character microscopically.

Substrate, Ecology and Season

This is a saprotroph of the ground layer, breaking down small woody debris, buried twigs, root fragments, leaf litter and mulch. It appears on shaded path edges, in gardens and allotments, in mulched borders, on woodland rides, in grassy places over old woody material, and on disturbed ground generally, including bare soil where wood has rotted below. It is not attached to a living tree and forms no mycorrhiza, which is why habitat is broad and the substrate connection runs downward to buried debris rather than outward to a partner tree.

Fruiting is chiefly late summer through late autumn, continuing until hard frost in mild seasons, and it favours a period of soaking rain. Fruit bodies come up in loose scattered troops, sometimes tens of them across a few metres, and individual mushrooms are ephemeral - up within a day, collapsing within two or three.

Separating the Look-alikes on Morphology Alone

Other brittlestems with plain gill edges. The genus is large and most members lack the coloured edge. Where a candidate has the same wiry stalk and hygrophanous cap but shows a plain whitish or concolorous gill edge under the lens, look at overall stature and the presence or absence of a rooting base to narrow it, and accept that many are not separable without microscopy.

Brittlestems with a fringed cap margin. Several relatives hang veil remnants as a white toothed fringe around the young cap margin and have broader, paler caps on stouter stalks. This species has at most a few fleeting fibrils.

Rooting brittlestems without red edges. Some species share the long pseudorrhiza but not the pigmented gill edge, so check both characters together rather than relying on the root alone.

Inkcaps and small parasols on mulch. Members of the inkcap group deliquesce into black liquid, or have pleated fan-like caps of few gills and paper-thin flesh. Neither happens here: the gills darken but stay intact and dry away.

Mottlegills. These have tougher, more rubbery, non-hygrophanous caps that stay grey-brown, distinctly mottled black gills, a jet-black spore print, and usually a grassland or dung-enriched habitat.

Small brown mushrooms with rusty prints. Any species giving a rusty or cinnamon print rather than a purple-black one is outside the genus regardless of how similar the habit looks.

Field Checklist

Very slender white brittle hollow stalk; small conical hygrophanous cap drying pale from the centre; striate margin; broad gills going purple-black with a fine pink to reddish edge; rooting base with white mycelium; dark purple-brown spore print; on litter, mulch and buried woody debris in autumn.