Yellowleg Bonnet Identification Guide

Standing Over It: The First Impression

You usually meet the Yellowleg Bonnet while you are looking at something else. It grows in deep springy needle litter under spruce and pine, in cushions of hair moss and Sphagnum, along the ragged edge of heather, and in wet grass at the woodland fringe, and the fruit bodies are so slight that a whole colony can read as nothing more than a scatter of pale pinheads on wires. The impression is of a tiny grey-brown parasol held up on a thread. What makes you stop and kneel is the stalk: a small bonnet with an obviously yellow stipe is uncommon enough to be worth a proper look, and this is the one you will meet most often.

Before touching anything, register three things. The cap is translucent enough that you can count the gill lines through it. The whole fruit body has a faint greasy shine after rain. And the stalk carries a lemon or greenish-yellow wash that looks out of place on an otherwise grey mushroom. Those three together already put you in the right corner of the genus.

Working Through the Cap

The cap is small, 5 to 20 mm across, occasionally a little more. It starts parabolic to narrowly conical, opens to bell-shaped, and finally settles low-convex with a broad, weak umbo. The margin is thin and often finely scalloped or crenulate, slightly incurved at first, later straightening and sometimes splitting or turning up in old, weathered material.

Colour is pale and cool: grey-brown with olive or yellow-green tints, darkest over the disc, thinning to cream or pale straw toward the edge. It is strongly hygrophanous, so a cap that dried on a sunny bank looks two shades paler than its neighbour under the moss. When moist the cap is translucent-striate, with the gill lines showing through as radial grooves that run almost to the centre. The surface is viscid to greasy in damp weather and merely tacky when dry.

The Peel Test That Settles the Group

This is the single most useful thing you can do in the field. The cap cuticle of this species is a separate gelatinous, elastic pellicle rather than a thin skin bonded to the flesh. Catch the margin between a fingernail and thumb, or use fine forceps, and lift. On a fresh specimen the whole skin comes away as one rubbery, translucent sheet that stretches noticeably before it tears, leaving the pale flesh bare beneath. Very few small bonnets do this so cleanly.

The same gelatinisation affects the gill edge. Lay a gill flat, run a pin or a needle along its extreme edge, and in fresh material the very margin of the gill detaches as a fine elastic thread that you can draw out for several millimetres. Try both tests on two or three fruit bodies, because rain-battered specimens lose the effect and a single failed attempt proves nothing.

Gills, Attachment and Colour

Around 15 to 25 gills reach the stipe, with shorter tiers between them, and the spacing is moderately distant, so the interspaces are easy to see. They are white to pale cream or faintly greyish, sometimes with a weak pinkish or buff flush in age, and the edges are concolorous or a shade paler.

Attachment matters. Split the whole mushroom vertically with a razor and look at the junction: the gills are adnate and then run a short distance down the stipe as a small decurrent tooth. They are not broadly decurrent. If the gills sweep well down the stem in a long curve, you are somewhere else in the genus.

The Stipe: The Feature the Name Points At

The stipe is 30 to 80 mm long, occasionally to 100, and only 1 to 2 mm thick. It is cylindrical and equal, hollow, elastic, smooth and polished, and when fresh it is coated with a thin slime layer that makes it slippery between the fingers.

The colour is the point. Expect lemon, sulphur or greenish yellow, usually strongest in the upper half and near the apex, fading to pale straw or dingy whitish downward. Some collections carry yellow along the entire length; others, after heavy rain has washed the gluten off, fade to nearly white. Judge from fresh, young, sheltered material and check several fruit bodies rather than one.

The extreme base is fastened into moss or needle litter by coarse white strigose hairs. Tease specimens out with a knife rather than pulling them, and those basal hairs stay intact for examination.

Base, Flesh, Colour Change and Odour

The flesh is very thin, pale and watery. Cut lengthwise and there is no colour change at all: no reddening, no browning, no blueing, and no latex. Any small bonnet that releases white droplets from a broken stipe belongs to a different group entirely. The odour is faint and inconstant, sometimes faintly chemical or iodine-like as material dries in a collecting box, often nothing at all.

Taking a Spore Print

The print is white, and because the caps are small and thin the deposit is faint. Cut the stipe flush with the gills, set two or three caps gills-down together on black card or on a strip of glass laid over black, cover them with an upturned tumbler to hold humidity, and leave them somewhere cool for four to eight hours. Pooling several caps is the difference between a readable print and a smudge.

Under the microscope the spores are smooth and ellipsoid, roughly 8 to 11 by 5 to 6.5 micrometres, and strongly amyloid in Melzer reagent, turning blue-black. That amyloid reaction is the standard confirmation for the genus and is worth running once if you have the equipment.

Substrate and Season

This is a litter-dwelling saprotroph, almost always terrestrial. Look on conifer needle beds under spruce, pine and larch, in moss cushions, among heather and bilberry, on peaty ground, and in damp grass at woodland margins. It occasionally appears on very rotten conifer wood and mossy stumps, which is worth knowing so that a specimen on wood does not throw you.

It is widespread across temperate and boreal Europe and North America, fruiting from late summer through late autumn and often persisting into the first frosts. Fruit bodies come in loose troops scattered through the moss rather than in tight tufted clusters, and the colonies follow the wettest, most sheltered pockets year after year.

Separating the Close Look-alikes on Structure Alone

• The variety viscosa, often met as a separate name, is larger and stouter, with a dark date-brown to reddish-brown cap instead of grey-olive, gills and stem base that stain reddish-brown, and a heavier glutinous coat. The peel test works on both.
• Mycena vulgaris is also viscid with a peelable pellicle, but its cap is a dull grey-brown, the gills are conspicuously decurrent rather than toothed, and the stipe is grey to brownish and never yellow.
• Mycena flavoalba puts the yellow in the cap, not the stalk: yellow to ivory cap, dry whitish stipe, and a preference for grassland and mossy lawns.
• Roridomyces roridus wears an extraordinarily thick clear gluten sheath on the stipe, far heavier than anything here, while its cap is dry, whitish and not peelable.
• The Mycena filopes and metata group have dry stipes with no separable skin; metata additionally carries pinkish tints in the cap.
• Mycena galopus bleeds white latex from a broken stem, which nothing in this group does.
• Mycena olivaceomarginata has olive-brown gill edges, a dry stem, and lives in short grassland.

Run the checks in this order and the identification tightens quickly: peel the cap skin, confirm a viscid yellow stipe, confirm a white print, and confirm conifer litter or moss.

Field Checklist

• Cap 5 to 20 mm, grey-brown with olive tones, translucent-striate, viscid.
• Cap skin lifts off as one elastic rubbery sheet.
• Gill edge separable as an elastic thread.
• Gills whitish, adnate with a short decurrent tooth.
• Stipe long, thread-thin, hollow, slimy, lemon to greenish yellow.
• Base with coarse white hairs binding moss and needles.
• Flesh unchanging, no latex.
• Spore print white, spores amyloid.
• Conifer litter, moss, heather; late summer to first frosts.