Brown Mottlegill

The Brown Mottlegill, Panaeolina foenisecii, is arguably the most frequently encountered lawn mushroom in temperate regions, appearing in scattered numbers on almost any regularly cut grass after rain. Its English names refer to that habit: it flushes just as the grass is being mown or hayed.

The genus Panaeolina was split from Panaeolus on microscopic grounds. Both share the mottled gill face produced by uneven spore ripening, but Panaeolina has warty, roughened spores and a dark brown rather than jet-black spore deposit. That combination of a mottled gill and a chocolate-brown print is the practical field signature of this species.

Because it is small, dull and hygrophanous, it changes appearance dramatically through a single day. A cap that was dark date-brown at dawn may be pale clay by mid-afternoon, usually with a distinct darker zone left along the margin, and beginners often record the wet and dry states as two different fungi.

Cap

The cap is 1 to 3 cm across, hemispherical to broadly convex or bluntly bell-shaped, never truly flat, and smooth to very finely wrinkled. Moist caps are dark reddish-brown or date-brown; as they lose water they dry from the centre outward to dull tan or greyish buff, leaving a darker band around the margin so the cap looks distinctly two-toned. The surface is dull rather than shining and is not viscid.

Gills

Gills are adnate, moderately broad and fairly well spaced. They begin pale greyish brown and darken to deep purplish or chocolate brown, and mature gill faces are unevenly blotched or mottled because the spores do not ripen simultaneously across the surface. Gill edges are finely whitish.

Stipe

The stipe is slender, 3 to 8 cm tall and 1 to 3 mm thick, straight, hollow, and pale buff to reddish brown, usually darker toward the base and often finely powdered near the apex. There is no ring and no volva, and the base has no bulb; fine white mycelial threads may bind grass roots at the point of attachment.

Flesh and spore print

The flesh is thin, pallid to watery brown, and does not change colour when cut or bruised. The spore print is dark brown, distinctly not black, and under the microscope the spores are roughened or warted with a germ pore, which is the character that places the fungus in Panaeolina rather than Panaeolus.

This mushroom is a grassland species, thriving in short, regularly mown or grazed turf: garden lawns, playing fields, churchyards, park grass, roadside verges, pastures and hay meadows. It favours turf that is at least moderately fertile and moist, and appears in scattered troops rather than tight clusters, often with several caps per square metre after warm rain.

The fruiting season is long, running from late spring through summer and into autumn, with the heaviest flushes in warm damp weather. It is one of the most cosmopolitan of all agarics, recorded throughout Europe, across North America, and in temperate and subtropical grassland worldwide, spreading readily with cultivated turf.

Panaeolina foenisecii is saprotrophic, feeding on dead grass roots, thatch and humus in the upper few centimetres of turf. It forms no mycorrhizal association with plants and does not attack living grass, instead recycling the accumulated organic litter that builds up beneath a mown sward.

Its rapid, repeated fruiting reflects a short-lived, opportunistic strategy. Mycelium spreads horizontally through the thatch layer and can produce successive flushes throughout the growing season whenever soil moisture and warmth coincide. Spores are dispersed by air, and the species travels easily with turf, topsoil and mown clippings, which explains its near-global presence in managed grassland.

The closest confusion is with true Panaeolus species that share the same lawns. Panaeolus cinctulus, the Banded Mottlegill, also dries with a darker marginal band but produces a jet-black spore print with smooth spores, and it tends to grow in richer, more manured or composted ground, often in denser clusters. Panaeolus fimicola and Panaeolus olivaceus are greyer or more olive-toned, more slender, and again give black prints.

Conocybe species in lawns can be similar in size but have conical, more brightly tawny caps on very fragile stipes and a rusty-brown spore print, quite different from the dull chocolate print here. Small Psathyrella species are more brittle with pale flaring stipes and often whitish veil fragments on the cap margin. Finally, Agaricus species in turf may look superficially brown but are far fleshier, with free gills passing from pink to dark brown and a distinct ring on the stipe, features the Brown Mottlegill never shows.