Platterful Mushroom Identification Guide

First impressions and the setting

The Platterful Mushroom is a mushroom of deciduous woodland floors, and it is usually spotted as a broad, flat, dull-coloured cap sitting slightly proud of the leaf litter. You are typically in beech, oak or mixed broadleaf woodland from late spring through to autumn, often near a mossy stump, along the line of a buried root, or on a fallen log already half-covered by litter.

The silhouette is characteristic: a wide cap, 5-15 cm and occasionally more, on a stem that looks too slender and too straight for the width it carries. The whole thing looks slightly flimsy, like a dinner plate balanced on a stick, and the flesh is genuinely thin for the cap diameter. That plate-on-a-stick outline plus a streaky grey-brown surface is the first impression to hold.

Reading the cap

Young caps are convex to bell-shaped with an inrolled margin; they expand quickly to broadly convex and then flat, sometimes with a low broad umbo and often with a wavy or upturned margin in age. Old caps split radially from the edge, which combined with the thin flesh gives a ragged, weather-beaten look.

The surface is the useful part. It is dry and matt, and it carries conspicuous radial fibrils, darker streaks of appressed fibres running from the centre outwards over a paler ground. Under a lens these look like fine brushed lines. Background colour ranges from pale grey-brown and mouse-grey through olive-brown to a darker sepia, and the streaks are always a shade or two darker. Some specimens are almost blackish-fibrillose over a grey ground; pale forms are nearly cream with brown streaking.

The cap is not viscid, not scaly, not zoned and not hygrophanous in a strongly two-tone way. Run a fingertip over it: dry and slightly silky.

Gills and the spore-bearing surface

Turn the cap over and the gills should stop you. They are strikingly broad, deep from edge to attachment, and widely spaced, so from below you see substantial gaps and a clean, uncluttered geometry. In a large specimen the full-length gills can be counted quickly, and they are interspersed with a few shorter ones.

Colour is white to cream, sometimes ageing to a dull off-white or faintly greyish, but never pink, never brown and never darkening dramatically. Attachment is adnexed to nearly free, notched where the gill meets the stipe, and the gill faces are smooth with even, entire edges. Gills tear cleanly and do not exude any fluid.

Stipe, base and the rhizomorph test

The stipe is 5-15 cm long, 1-2 cm thick, cylindrical or slightly swollen below, and white to greyish-white, often with fine longitudinal grey fibrils that echo the cap streaking. It is dry, without a ring and without a volva, and it is notably tough and fibrous: twist it and it shreds lengthways rather than snapping, and it usually turns out to be hollow or stuffed with a pith.

The base is where the identification is won. Do not pull the mushroom out. Cut down into the litter around the base with a knife and lift the whole stem with its surrounding debris. You should find thick, white, cord-like rhizomorphs radiating from the stem base into the leaf litter and running away to buried wood, sometimes for tens of centimetres. They look like white shoelaces or fine roots, they are tough, and they are often branched.

These rhizomorphs are the single most reliable character. Very few pale-gilled woodland mushrooms of this size have them, and they instantly explain why a mushroom that appears to grow from soil is in fact a wood-decayer feeding on buried timber.

Flesh, odour and colour change

The flesh is white, thin, soft in the cap and fibrous in the stipe. Cut a fruit body in half from cap edge to stem base and leave it exposed for several minutes. There is no bluing, no reddening, no yellowing and no blackening; at most the cut surface dulls very slightly. No latex is produced. Odour is mild and faintly mushroomy, without any radish, mealy or aniseed note.

Taking and reading a spore print

This species prints easily because the caps are large and drop heavily. Cut a fully expanded but firm cap free of the stipe, set it gill-side down on paper, cover it with a bowl and leave it two to four hours or overnight.

The print is white. Because the gills are so widely spaced, the deposit shows as bold, well-separated rays rather than a solid disc, which is itself a small confirmation of the gill spacing you noted in the field. Read it against a dark background to be certain there is no pink flush, because the main look-alike group has a pink to salmon print and the difference can be subtle in a thin deposit.

Substrate, season and ecology

Megacollybia platyphylla is a saprotroph causing white rot in dead hardwood. It fruits on and around decaying stumps, fallen logs, large buried roots and wood fragments hidden under the litter, and much of the time the substrate is invisible until you dig. Beech and oak are common hosts in Europe; related species in North America occupy the same niche on eastern hardwoods.

Season runs from late spring to autumn, earlier than many woodland agarics, with a strong early-summer showing after rain. Fruit bodies are usually solitary or in small scattered groups rather than dense tufts, and they degrade fast, going soft and ragged within days.

A note on the group: the eastern North American populations are now treated as separate species, notably Megacollybia rodmanii, separated on microscopic and molecular grounds rather than by any field character. Everything in this guide applies to the group as a whole.

Separating it from look-alikes on morphology alone

Deer Shield (Pluteus cervinus). The most frequent confusion, and it shares a streaky brown cap and a woodland-wood habit. Separate on three points: its gills are truly free with a clear gutter around the stem and they flush distinctly pink as they mature, its spore print is pink to salmon, and it has no white rhizomorphs at the base. The Platterful has notched, white, unchanging gills, a white print and conspicuous cords.

Rooting Shank (Hymenopellis radicata and relatives). Similar broad distant white gills and a slender stem, but the cap is viscid and radially wrinkled rather than dry and fibrillose, and the stem base tapers into a long tough taproot that plunges deep into the soil. A root, not a spray of surface cords.

Tricholoma species. Also white-gilled with white prints, but they grow on soil with living trees, have thicker fleshy caps, notched gills that are usually crowded rather than widely spaced, and no rhizomorphs.

Entoloma species. Grey-brown streaky caps occur in this genus too, but the gills turn salmon-pink and the spore print is pink, and most grow from soil in grassland or woodland without wood cords.

Clitocybula and small grey Collybioid species. Much smaller, with crowded gills and often decurrent attachment, and lacking the plate-like proportions.

Melanoleuca species. Flat caps on straight stems can look similar, but their gills are crowded and narrow rather than broad and distant, and they favour open grassy or disturbed ground.

A quick field sequence

Wide flat streaky grey-brown cap on a slender straight stem, in broadleaf litter. Gills broad, distant, white, notched. Stipe tough and fibrous, hollow, no ring, no volva. Dig the base and find white cord-like rhizomorphs into buried wood. No colour change on cutting. White spore print. That combination is the Platterful Mushroom.