Pluteus admirabilis Identification Guide

First Impression and Setting

You find this one by looking down at decaying wood in summer. The typical encounter is in damp deciduous woodland, on a soft, well-rotted log of maple, elm, beech or birch that has lost its bark and gone spongy, often mossy on top. Scattered across it are small, fragile mushrooms 1 to 3 cm across whose caps are a warm golden or honey yellow, bright enough to look almost artificial against wet brown wood. They are thin-fleshed and slightly translucent when soaked, and a group may include a dozen individuals of different ages, some still bell-shaped, some already flat. Nothing about the growth habit is clustered or tufted; each fruit body arises separately from the wood surface.

Reading the Cap

Start at the centre. The disc is typically the deepest colour, tawny to golden-yellow or slightly brownish-yellow, and it is usually distinctly wrinkled, veined or rugulose, as though the surface had been pressed and released. Outwards the colour lightens to clear yellow and the wrinkles fade. The cap shape passes from conical or convex through broadly convex to plane, often keeping a low umbo. The surface is moist but not slimy, and the flesh is hygrophanous: wet caps are translucent and show radial striations that mark the position of the gills beneath, while drying caps become paler, more matt and lose the striation. Because the whole thing is only a couple of centimetres wide, a hand lens is worth using to see the wrinkling clearly.

The Gills and the Free-Attachment Test

This is the character that puts the species in Pluteus and it must be checked deliberately. Slice a fruit body vertically down the middle, or simply look under a mature cap from the side. The gills stop short of the stipe, leaving a narrow clear channel all the way around the stipe apex; they are not attached to it at any point. They are crowded, moderately broad, ventricose, and their colour is a story in itself: whitish or pale yellowish in very young buttons, then progressively flesh-pink, salmon and finally a dull rose-brown as the spores ripen. The edges are paler than the faces and finely fringed under a lens. If a small yellow mushroom on wood has gills that run onto the stipe or notch into it, it is not this species.

The Stipe and Base

The stipe is 2 to 5 cm tall and only 1 to 3 mm thick, equal or barely widening downwards, smooth to slightly silky, and clear yellow along most of its length, sometimes paler at the very apex and often more intensely yellow at the base. There is no ring, no ring zone, and no volva or sac at the bottom. Ease the base out of the rotten wood rather than snapping it: you should find a small pad of white mycelium binding wood fibres, and no bulb, no cup and no rooting extension. A yellow stipe paired with a yellow cap is the diagnostic combination here, and it is worth photographing while fresh because the colour can wash out within a day.

Flesh and Colour Change

The flesh is very thin, pale yellowish in the cap and yellow in the stipe, and it does not change colour on cutting or bruising. There is no latex, no blueing, no reddening. Handled specimens may darken slightly and dry ones fade, but neither is a true bruising reaction.

Taking a Spore Print

Small caps still print well if you give them humidity. Detach the cap, place it gills-down on white paper, cover with a small container, and leave it for four to eight hours. The deposit is pinkish, ranging from pale salmon to a fuller flesh-pink in a heavy print, and it is best judged by scraping the powder into a small heap with a blade. Pink spores plus free gills plus a ringless, volvaless stipe is the Pluteus signature, and it removes the yellow-capped species in every brown-spored and white-spored genus at once. Microscopically the spores are small, smooth, broadly ellipsoid to nearly globose.

Substrate and Season

This is a saprotroph of decayed deciduous wood. Look for soft, wet, bark-free logs and large branches in the later stages of decay, standing stumps that have gone crumbly, sawdust and woodchip, and occasionally buried wood in leaf litter where the fruit body appears to spring from soil. The season runs from early summer into autumn, with the best flushes a few days after prolonged rain in warm weather. It is a mushroom of humid, shaded woodland rather than exposed edges, and it dries out and collapses fast once conditions turn.

Separating It From Look-alikes

• Pluteus romellii is the classic confusion and it is settled by comparing cap and stipe. Romelli's species has a distinctly brown to olive-brown cap over a bright yellow stipe; here both cap and stipe are yellow.
• Pluteus leoninus is larger, with a yellow cap that browns towards the centre and, crucially, a whitish to pale grey stipe rather than a yellow one.
• Pluteus chrysophaeus and its allies have brownish-yellow to olive-brown wrinkled caps and pale stipes.
• Bolbitius titubans is superficially similar in colour but has a viscid, extremely fragile, soon-collapsing cap with a strongly grooved margin, gills that are attached rather than free, a rusty cinnamon spore print, and a preference for grass, straw and dung.
• Leucocoprinus birnbaumii is bright yellow and powdery, with a strongly pleated cap, a distinct ring on the stipe, a white spore print, and a habit of appearing in plant pots and greenhouse soil.
• Small yellow Gymnopilus and Flammulaster species drop rusty brown spores and have attached gills.
• Entoloma species also print pink but their gills are attached to the stipe and their spores are angular under the microscope.

Microscopic Confirmation

If you take it further, look at the gill edge and face. The cheilocystidia are abundant, thin-walled and clavate to bottle-shaped, while the pleurocystidia are thin-walled and lack the thick walls and apical hooks of the metuloid-bearing Pluteus group. The cap surface is a hymeniderm of inflated club-shaped to pear-shaped cells, which is what makes the disc look wrinkled to the naked eye.

Field Checklist

On well-rotted deciduous wood; cap 1 to 3 cm, golden yellow, wrinkled at the centre, hygrophanous; gills free, white then pink; stipe slender and yellow, no ring, no volva; flesh unchanging; spore print pink; summer to autumn.