Haymaker's Mushroom Identification Guide

The First Impression

This is the small brown mushroom of the mown lawn, and it is probably the one you have walked past most often. The setting is grass: a garden lawn, a playing field, a churchyard, a grazed pasture, a roadside verge. Fruitbodies come up scattered or in loose troops a day or two after rain, most abundantly in the weeks when the grass is being cut regularly, which is where the common name comes from.

At a glance you see a thin, wiry stem holding up a small domed cap somewhere between milk-chocolate and pale biscuit. The single most useful first impression is that the cap colour is not uniform across the troop, and often not even across one cap. Some fruitbodies are dark and saturated, others are pale and dull, and many are dark at the margin with a paler zone spreading from the centre. That is hygrophanous drying in action, and once you learn to read it you can pick this species out from across a lawn.

Reading the Cap

Caps run 1 to 3 cm across, occasionally reaching 4. The young shape is hemispherical, becoming broadly convex and finally almost flat or gently bell-shaped, without a sharp umbo. The surface is smooth to the naked eye, never scaly and never sticky. Under a lens, a fresh moist cap looks minutely and finely mealy or pruinose rather than polished.

Moist, the cap is a deep date-brown to dull reddish-brown, sometimes almost purplish-brown. As it loses water it fades from the centre outward to tan, clay-buff or pale greyish-brown. During drying you frequently see a distinct two-toned pattern: a paler disc with a broad darker band around the margin, occasionally with a fine paler line at the very rim. That banded, drying-in-progress look is diagnostic enough to stop you and check the rest.

The margin is not translucently striate when moist, or only faintly so at the extreme edge, which is a useful negative character. If your cap is deeply lined so that the gills show through as ribs, you are probably looking at something else. Also note what is absent: there are no veil remnants hanging from the rim, no fibrils and no ring on the stem.

Gills, Stipe and Flesh

Turn one over. Gills are adnate, sometimes with a small notch, moderately broad and fairly well spaced compared with a Psathyrella. Their colour progression is the key: pale greyish-brown when young, then deepening to a dull brown flushed with purple, and finally dark chocolate to purplish-brown. Watch for faint mottling, an uneven patchy darkening caused by spores maturing in patches rather than uniformly. In this species the mottling is present but subdued; it is not the strongly blotched, marbled surface of a true Panaeolus. Under a lens the gill edges are usually finely whitish and slightly ragged.

The stipe is 4 to 8 cm long and 1.5 to 3 mm thick, straight, slender, more or less equal, and hollow. It is whitish at first, becoming dull brown from the base upward with age, sometimes with a slight pinkish tinge, and it is smooth or very finely pruinose near the apex. It is brittle and snaps cleanly rather than shredding into fibres. There is no ring, no ring zone, no volva and no bulb, though the extreme base may carry a wisp of white mycelium bound into the grass thatch.

The flesh is thin, pale brown and watery, with no distinct colour change when cut. Any strong colour reaction in the flesh or stipe points away from this species. The smell is faint and mushroomy at most, not distinctive.

Taking and Reading a Spore Print

This is the step that closes the identification, and it is worth doing properly because the entire lawn-mushroom problem turns on print colour. Take a fully expanded cap that has already darkened its gills, trim the stipe flush, and lay the cap gills-down on white paper under a glass for two to four hours. The caps are small, so use two or three at once to build a readable deposit.

The print is dark brown with a clear purplish or vinaceous component, often described as chocolate or purple-brown. Crucially it is not jet black. Look at it against white in good daylight, and smear a little with a fingertip: black-spored species leave a neutral grey-black smear, while this leaves a warm brown-purple one.

Under a microscope you get the genus character. Spores are 12 to 17 micrometres long by 7 to 9 wide, lemon-shaped to broadly ellipsoid, with a germ pore, and their walls are distinctly roughened, warted or minutely wrinkled. That ornamentation is what separates Panaeolina from Panaeolus, whose spores are smooth and jet black in deposit. If you have a microscope, this is a five-minute confirmation.

Substrate, Season and Ecology

The substrate is grassland thatch: the layer of dead stems, clippings and roots at the base of a living sward. This is a saprotroph, decomposing that material, and it is not mycorrhizal and not tied to dung, though it will grow happily on well-manured pasture. It is one of the earliest grassland species of the year, appearing from late spring, and continues in flushes through summer and into autumn wherever moisture allows.

Regular mowing suits it, because clipping constantly renews the supply of decaying grass at the soil surface. Expect it in short, frequently cut turf far more than in long rough grass, and in lawns that are moderately fertile rather than nutrient-poor. Its abundance in gardens and parks makes it a good species to learn early, since it is the baseline against which every other lawn mushroom gets compared.

Separating It From Look-alikes

Panaeolus species share the grassland habitat and the mottled gills. Separate them on print colour first: Panaeolus gives a jet-black deposit and has smooth spores. Panaeolus papilionaceus is also more strongly bell-shaped, keeps a fringe of white veil teeth along the cap margin, and is more strictly associated with dung. Panaeolus fimicola is greyer and more dung-linked.

Psathyrella species can look similar but are more fragile, with a stipe that is conspicuously white and brittle, a cap margin that is usually more translucently striate when wet, and gills that are less mottled. Prints are dark brown to blackish-brown but the fruitbodies fall apart at a touch.

Conocybe species in the same lawns have a more sharply conical or acorn-shaped cap on a very thin, often shining stipe, and their spore print is a warm rusty ochre-brown with no purple component at all. That colour difference is unmistakable side by side.

Agrocybe pediades is a grassland species with a smoother, more ochre-yellow to tan cap that is less strongly hygrophanous, a firmer stipe, and a dull brown print lacking purple tones.

Bolbitius titubans is yellow when young, extremely fragile, and gives a rusty print. Marasmius oreades, the other classic lawn mushroom, has a tough pliant stipe, widely spaced pale gills and a white spore print, which rules it out immediately.

Field Checklist

Small smooth cap, hemispherical to convex, strongly hygrophanous and often two-toned while drying; adnate, faintly mottled gills going dull purple-brown; slender hollow brittle stipe, no ring; purplish chocolate-brown spore print; roughened lemon-shaped spores; growing in mown grassland thatch from late spring onward.