Brown Mottlegill Identification Guide

The Setting: Mown Grass After Rain

This is the archetypal lawn mushroom, and its habitat is a genuine identification character rather than background scenery. Panaeolina foenisecii appears in short, regularly cut grass: garden lawns, playing fields, verges, cemeteries, park turf, pasture margins and the grassy strips between paths. It comes up in numbers a day or two after warm rain, often scattered in loose troops of dozens across a few square metres, and it can be gone within forty-eight hours. It is saprotrophic, feeding on the thatch of dead grass stems, roots and organic matter in the top few centimetres of soil, so it needs no trees and no wood. It also does not require dung, even though several of its relatives do, and finding it in the middle of a well-kept lawn far from any animal droppings is entirely normal.

The First Impression

Small, brown, and slightly conical on a wiry stem. What catches the eye across a lawn is usually the two-tone effect: on a drying morning a scattered population shows caps that are pale tan across the top and distinctly darker around the outer band, so the field looks as though someone has painted rings on it. Individually they are unimpressive — 1 to 3 cm caps on stems no thicker than a matchstick — but as a group they are visually consistent, and consistency across many fruitbodies of different ages is exactly what you want when identifying small brown mushrooms.

Reading the Cap

Measure first: 1 to 3 cm across, occasionally 4. The shape starts as a rounded cone or a low bell and expands only partly, so most mature caps remain broadly conical to bluntly bell-shaped, sometimes with a slight central hump, and rarely become truly flat. The margin is even and not grooved, though in very moist material a faint translucent striping may show near the edge.

The defining cap character is hygrophany — the way colour tracks water content. Fully moist, the cap is a rich date-brown, chestnut or dark reddish-brown. As it dries it pales from the centre outward to a dull tan, clay or greyish-buff, and while drying is in progress there is a clear boundary between the pale dried centre and the still-dark outer zone. That drying front is the two-tone banding, and it is one of the most useful things to look for. The surface is smooth, matt and dry to the touch, sometimes minutely wrinkled around the centre in age, and it has no scales, no slime and no veil fragments hanging from the rim.

The Gills and the Mottling

This is the character the common name is built on, so take your time. Tilt the cap and look along the gills rather than straight at them. They are moderately broad, fairly widely spaced, and attached to the stipe by a narrow adnate join or slightly notched. Young gills are pale greyish-brown or clay coloured. As the spores ripen they darken, but — and this is the point — they ripen unevenly, in patches, so a mature gill face becomes a mosaic of dark chocolate blotches over a paler ground. The effect is genuinely mottled, like weathered stone. Look at the gill edges under a lens as well: they are typically finer and paler than the faces, appearing as a thin whitish line running the length of each gill.

The Stipe, Base and Flesh

The stipe is 3 to 8 cm tall and only 1 to 3 mm thick, straight or slightly wavy, hollow, and brittle enough that it snaps cleanly rather than tearing. It is pale brown to reddish-brown, usually paler and finely powdered or frosted near the apex and darker towards the base. There is no ring, no ring zone and no veil remnant of any kind — an important negative character. The base is simple, sometimes with a few pale fibrils binding grass roots, and there is never a bulb or a sac. Cut a fruitbody lengthwise: the flesh is thin, watery brown, and does not change colour when exposed to air. No latex, no blueing, no reddening.

Taking and Reading the Spore Print

Because almost every character above is shared with some other small brown lawn mushroom, the spore print is what closes the case. Snap the stipe off flush with the gills, place the cap gill-side down on paper, and cover it with a small glass or cup. These caps are thin and dry out fast, so add a drop of water beside the cap under the cover to keep the air humid, and choose a cap that is fully expanded and dark-gilled. Two to four hours usually suffices.

Read the deposit on white paper first, then on black or foil. Panaeolina foenisecii gives a dark brown print — a deep chocolate or dull umber brown, sometimes described as purplish-tinged but never truly black and never rusty. Comparing side by side with a second print is the reliable way to judge this; brown against black paper looks blacker than it is. Under a microscope the spores are ornamented with fine warts, which is the genus-level distinction from smooth-spored relatives, and they are lemon-shaped with a distinct germ pore.

Season and Ecology

Fruiting runs from late spring through to autumn, with the heaviest flushes in warm, wet spells from May to September. The species is a grassland decomposer working on thatch and buried plant debris, and it is favoured by regular mowing, which continually supplies dead material at the soil surface. It is not host-specific and needs no tree partner. Populations recur in the same lawn year after year, often in the same patches, marking where the underground mycelium has established.

Separating It From Look-alikes on Morphology

True Panaeolus species share the mottled gills but differ in the print: theirs is jet black rather than brown, and several of them, such as Panaeolus papilionaceus, carry small whitish veil teeth hanging around the cap margin and grow directly on dung rather than in lawn thatch. Psathyrella species are more fragile still, with paler, more greyish or whitish caps, often visible veil fibres at the margin, and a purple-brown to blackish print, and most fruit on or near buried wood. Conocybe species are conical and slender like this one but far more delicate, with a rusty cinnamon print and smooth, evenly coloured gills that never mottle. Agrocybe pediades is another grassland species but has a smoother, more hemispherical, slightly tacky ochre cap and a cinnamon-brown print with unmottled gills. Marasmius oreades shares the lawn but has a tough, pliant stipe you can twist without breaking, well-spaced pale gills that are nearly free of the stipe, and a white spore print. In short: mottled gills plus a dark brown print plus a hygrophanous two-tone cap plus a ringless brittle stem in mown grass is a combination none of these can match.

Quick Field Checklist

Small conical to bell-shaped cap drying in two tones from the centre; broad, unevenly darkening, blotchy gills with pale edges; slim brittle ringless stipe frosted at the apex; unchanging watery brown flesh; dark chocolate-brown spore print; scattered in mown grass after rain.