St. George's Mushroom Identification Guide

The First Impression

Late April, an old pasture or a chalk-downland verge, and a curved line of white domes pushing up through short turf. Often the grass along that line is a darker green than the sward around it. The mushrooms are chunky and solid, their caps cream to white, their margins rolled tightly under, and they sit low with thick stems buried in the thatch.

Everything about the encounter says spring grassland: the season, the arc, the firmness. Very few substantial white grassland mushrooms are out this early, and that fact alone narrows the possibilities enormously before you touch anything.

Reading the Cap

Caps run 4-12 cm across, sometimes to 15 cm on well-grown specimens. Young ones are hemispherical, almost like a hard bun, with a strongly inrolled margin that stays curved under for a long time. With expansion the cap becomes broadly convex and finally flat or slightly depressed, and it frequently develops an irregular, lobed or wavy outline rather than staying neatly circular.

The surface is dry and matt, smooth to very faintly suede-like, with the feel of soft kid leather. It is never viscid, never scaly, never striate at the margin. Colour is white to cream when fresh, ageing to pale buff, ochre-cream or a light tan over the disc. In dry weather the cap surface often cracks into shallow patches.

The Gills

Turn a cap over and look carefully at where the gills meet the stem. They are emarginate — notched, with a small upward curve of the gill edge just before it reaches the stem — rather than running down it or being cleanly free.

Beyond attachment, the gills are extremely crowded, narrow, thin and even-edged. Colour is white to cream, at most becoming faintly buff with age. They never go pink, never brown, never grey. This is a point to check twice, because the main look-alikes betray themselves precisely here.

Stipe, Base and Flesh

The stem is short and thick relative to the cap: roughly 3-8 cm long and 1.5-3 cm wide, cylindric or thickened toward the base into a club. It is white, solid and firm all the way through, with a faintly fibrillose surface and a slightly powdery apex. There is no ring, no ring zone and no volva. Splitting the stem lengthwise shows dense, fibrous white tissue with no hollow.

Excavate the base rather than snapping the mushroom off at ground level. It usually comes up with a plug of soil and grass roots bound together by white mycelium, and there is no bulb, no sac and no swelling of any distinctive shape.

Now cut the cap in half and immediately smell the fresh break. The odour is strongly farinaceous: fresh flour, crushed grain, or the smell of cut cucumber rind. It is one of the strongest and most consistent field characters this species has, and in a good specimen you can smell it from arm's length. The flesh itself is thick, white and firm, and it does not change colour on exposure.

Taking a Spore Print

Cut the stem off flush and lay the cap gill-side down on a dark surface or a glass slide, covered with a bowl. These are thick, moist caps and they print generously within a few hours.

The result should be white to very faintly cream. The reason this matters so much is that the two closest confusions in the same habitat and season are pink-spored, and a print settles them instantly. Because a white print is invisible on white paper, always use black card or glass over a dark cloth.

Under the microscope the spores are notably small — around 4.5-6 x 2.5-3.5 micrometres — smooth, ellipsoid and inamyloid, with none of the angular outline seen in Entoloma. A further confirming detail for those with the stains available is that the basidia contain siderophilous granules, a character of the family Lyophyllaceae to which the genus belongs.

Substrate, Season and Ecology

This is a grassland saprotroph, living on the accumulated thatch and organic matter in old undisturbed turf. Its typical settings are unimproved pasture, chalk and limestone downland, roadside verges, churchyards, dune grassland, hedge banks and the grassy fringes of woodland rides. Calcareous soils are especially productive.

It fruits from mid-April through May and into June, earlier in mild springs. The mycelium grows outward as a circular patch, so fruit bodies appear in arcs, rings and rows, and the same ring reappears in the same place year after year, expanding slowly. The stimulated grass along the fruiting line is often visibly greener and more vigorous, since the mycelium liberates nitrogen as it decomposes the thatch.

Separating the Look-Alikes on Morphology

Entoloma clypeatum. The most important comparison, because it shares the season and often the hedgerow habitat, growing in association with rosaceous trees and shrubs such as hawthorn, blackthorn and plum. It differs in nearly every detail once examined: the cap is greyish brown rather than cream, hygrophanous and often radially fibrillose with a distinct umbo; the gills turn salmon-pink as spores mature; the flesh is thinner; the stem is more slender and often fibrous-twisted; and the spore print is pink, with angular spores under the microscope.

Entoloma sinuatum. Larger and paler, grey-buff to ivory, with a notched gill attachment much like Calocybe, but the gills pass from yellowish to pink and the spore print is pink. It is also a summer-to-autumn fungus of woodland edges rather than a spring grassland one.

Clitopilus prunulus. White and mealy-smelling as well, so it deceives on odour, but the gills are distinctly decurrent, running down the stem, the cap surface is soft and felted like suede, the flesh is thin, and the spore print is pink. It is a late-summer and autumn woodland species.

Agaricus species such as A. campestris. Gills are free from the stem and pass through bright pink to chocolate brown, there is a ring on the stem, and the spore print is dark brown. They also fruit later in the year.

Leucoagaricus leucothites. White, grassland-dwelling and firm, but with free gills, a movable ring on the stem, and a pinkish-cream spore print.

White Clitocybe species of grassland. These have decurrent gills, thinner flesh, smaller and more flattened or funnel-shaped caps, and appear mainly in late summer and autumn.

Melanoleuca species. Flatter caps, usually darker brown, a comparatively long slender stem, and microscopically ornamented amyloid spores.

Quick Field Checklist

• Spring, mid-April to June, in old grassland, verges and downland
• Growing in arcs and rings, often with greener grass along the line
• Cap 4-12 cm, cream to white, dry and matt, margin long inrolled, outline often lobed
• Gills crowded, narrow, notched at the stem, staying white to cream
• Stem short, thick, solid white, without ring or volva
• Flesh thick, white, unchanging, with a powerful mealy odour
• Spore print white; spores very small, smooth, not angular