Willow Shield Identification Guide

The first impression and the setting

Willow Shield is a wood-inhabiting mushroom of damp deciduous woodland, and you almost always find it in the right context: a rotting willow log lying in a wet hollow, a fallen alder in a carr, a mossy stump on a riverbank, or a pile of decaying deciduous branches in a damp shady corner. The mushroom itself is modest, three to seven centimetres across, with a greyish cap that reads as cool and slightly steely against the brown of the wood.

What makes you stop is usually the gill colour. From below, a mature specimen shows salmon-pink gills that clearly do not touch the stem, and that single observation - free gills, pink, on wood - narrows things down enormously before you have picked it.

Reading the cap

The cap begins convex, sometimes almost bell-shaped, and flattens with age to broadly convex or plane, often keeping a low broad umbo. The colour is a cool grey: grey-brown, ash-grey, sometimes with an olive or greenish-grey wash, occasionally darker and more sooty at the centre. There is little of the warm tan or fawn tone of the commonest members of the genus.

Look at the centre with a lens. In this species the disc is finely granular-scaly or minutely scurfy, with small dark scales or fibrils breaking up the surface, while the outer half of the cap is much smoother and often finely radially fibrillose. In wet weather the margin may become slightly striate, showing the outline of the gills beneath as faint radial lines. The cuticle is dry to very slightly greasy, not viscid.

Cap margin: even at first, often becoming slightly wavy or upturned in old specimens. There is no veil remnant on the margin, no ring zone, no volval patches.

The gills

Gills are the diagnostic organ in this genus and must be examined properly. Turn the mushroom over and look at where the gills meet the stem.

They are free: each gill stops short of the stipe, leaving a narrow gutter or moat of clear space all round it. This is best seen by slicing the mushroom lengthways with a knife, when the gills are seen to end in mid-air rather than running onto the stem. They are crowded, moderately broad, and ventricose (bellied) in profile, with several tiers of shorter gills interleaved between the full-length ones.

Colour changes with age and is a timing clue. Young gills are white to pale greyish. As the spores mature they flush pale pink, then a distinctly salmon or flesh-pink, and finally a duller brownish pink in over-mature specimens. The gill edge is usually slightly paler than the face and may look minutely fringed under a lens.

Stipe, base, flesh and colour change

The stipe is central, more or less equal or slightly thickened downwards, typically four to eight centimetres tall and four to eight millimetres thick. It is whitish to pale grey and finely fibrillose, sometimes with darker grey longitudinal fibrils on a paler ground. Critically, there is no ring and no volva: the stipe emerges cleanly from the wood, and the very base may be slightly swollen or padded with white mycelium binding wood fibres.

The base is where the most useful supporting character sits. In this species the lower stipe and base often develop bluish, blue-green or greenish tints, sometimes present when fresh and sometimes appearing where the mushroom has been handled, bruised or cut, and typically strengthening as the collection sits in a basket. It can be subtle - a cool teal cast rather than a bright blue - so examine the base in good light and scratch it lightly to watch for a slow change. Not every specimen shows it strongly, so its absence does not rule the species out, but its presence in a grey Pluteus on damp deciduous wood is very telling.

The flesh is thin, white to greyish, soft and fragile, without any distinct colour change through the cap. There is no latex.

Taking and reading a spore print

A spore print is essential here, and it is easy. Cut the stipe flush, set the cap gills-down on white paper, cover it with a cup or bowl to keep humidity up, and leave it two to four hours; a mature cap can deposit in less.

The print is pink: a clear salmon or flesh-pink, sometimes with a slight brownish cast in older material. Use white paper rather than black, since pink shows poorly against dark backgrounds. A white print rules the species out entirely, as does a rusty-brown or purple-brown one.

Under the microscope the spores are smooth, broadly ellipsoid to subglobose and thin-walled, and the cheilocystidia on the gill edge are abundant, thin-walled and club-shaped to bottle-shaped, while the pleurocystidia on the gill face are thick-walled with hooks or horns at the apex - the classic metuloid form of the genus.

Substrate and season

This is a saprotrophic species of dead deciduous wood, decaying it in place. Willow and alder are the classic hosts, matching the name, but it also occurs on poplar, ash, beech, birch and other broadleaves, and on buried wood, wood chips and sawdust piles where those are present. It is a species of damp ground, so the habitats to search are floodplain woodland, willow carr, riverside strips, damp mixed woodland and shaded ditches.

Fruiting runs from early summer through autumn, with peak appearances after warm wet spells. Fruit bodies are typically solitary or in small groups of two or three rather than large troops, and they are short-lived, collapsing within a few days.

Separating it from the look-alikes

Pluteus cervinus, the commonest relative, is larger and more robust, with a warm deer-brown to dark brown cap that is radially fibrillose rather than granular-scaly at the centre, and it lacks any bluish-green tinting at the base. Colour and stature separate most collections.

Pluteus umbrosus has a dark brown cap with a strongly veined and wrinkled centre and, decisively, dark brown gill edges visible with a lens.

Pluteus podospileus and its relatives are much smaller, with a dark velvety-granular cap centre and a stipe finely dotted with dark scurf, and no greenish tones.

Pluteus plautus in the broad sense is greyish and can look very similar, but has a more distinctly granular-pruinose cap and stipe surface throughout and lacks the blue-green basal tinting.

Entoloma species also give pink spore prints, but their gills are attached to the stipe, usually adnate to sinuate or decurrent, and they grow from soil rather than wood. Any pink-spored mushroom rooted in soil with attached gills should be worked as an Entoloma.

Volvariella and Volvopluteus share free gills and pink spores but always have a sac-like volva at the stipe base; dig carefully, because a shallow volva is easily left behind in the substrate.

Young Amanita species have free gills but produce white spore prints and carry a volva, a ring or both.

Quick field checklist

Grey to olive-grey cap with a finely scaly centre, crowded free gills turning salmon-pink, a ringless whitish stipe with bluish-green tints low down, growing directly on rotting deciduous wood in damp woodland, with a pink spore print. Confirm all five before settling on the name.