Willow Shield

Pluteus salicinus belongs to the shield mushrooms, a large genus of wood-inhabiting agarics defined by three consistent features: gills that are entirely free from the stem, a pink to pinkish-brown spore print, and the absence of any ring or volva. The genus sits in the Pluteaceae alongside Volvariella, which shares the pink spores but has a bag-like volva at the stem base.

Within the genus, Pluteus salicinus is one of the readily recognised grey-capped species. It is smaller and more slender than the common Deer Shield, and its cap carries distinctly cool tones: grey, bluish-grey, or grey with an olive or greenish cast, usually darker and finely granular or scurfy over the centre. The stem is white to greyish and frequently develops blue-green tints toward the base, particularly where it has been handled or damaged.

As the English name suggests, it is closely tied to damp riverside woodland and the soft hardwoods that grow there. It is a saprotroph on small dead wood rather than a partner of living trees, so it appears on fallen twigs, buried sticks and rotting stumps rather than out on open soil.

Cap

2-7 cm across, conical to bell-shaped when young, expanding to convex and finally flat, often with a low broad umbo. The surface is grey, blue-grey, ash-grey or grey with an olive-green tinge, darkest at the centre where it is finely scurfy, granular or minutely scaly; toward the margin it is smoother and radially fibrillose, and the extreme edge may be faintly striate when moist.

Gills

Free from the stem, leaving a clear gap around it, crowded and fairly broad. They are white at first, then pale pink and finally salmon or flesh-pink as the spores ripen. The gill edges are even and often slightly paler than the faces.

Stipe

3-8 cm long, 0.3-0.8 cm thick, roughly equal or slightly swollen at the base, white to pale greyish and finely fibrillose, frequently marked with fine dark fibres. Blue-green to turquoise tints often develop at the base and on bruised areas. There is no ring and no volva.

Flesh and spore print

The flesh is white and thin, sometimes taking on greenish-blue tones in the stem base where cut or bruised. The spore print is pink to pinkish-buff, an essential confirmation for the genus; spores are smooth and broadly ellipsoid.

Pluteus salicinus is a fungus of damp, shaded broadleaved woodland, especially along rivers, streams and in carr and floodplain forest. It fruits on dead wood of soft hardwoods, above all willow, alder and poplar, and also on ash, elm, hazel and beech. Typical substrates are fallen branches, half-buried sticks, rotting stumps and chunks of decayed wood lying among leaf litter, and fruit bodies sometimes appear to arise from soil when the wood beneath is buried.

Fruiting runs from early summer to late autumn, with the most reliable flushes after summer rain. The species is widespread across temperate Europe and temperate Asia and occurs in North America, being most frequent in low-lying, moist habitats and generally absent from dry upland woods.

This is a saprotrophic white-rot fungus. It decomposes small- and medium-diameter hardwood, degrading lignin and cellulose and reducing fallen willow and alder branches to soft, pale, crumbling fibre. Because willow carr and riverside woodland shed large quantities of small dead wood, the habitat provides an abundant and constantly renewed substrate.

Shield mushrooms as a group are almost entirely wood-associated saprotrophs, with no mycorrhizal partners, which is why they can fruit inside dense shade and on isolated pieces of wood far from any particular tree species. Their fleshy, quick-growing fruit bodies exploit short humid windows and then collapse, supporting a range of fungus gnats and beetles in the process.

Pluteus cervinus, the Deer Shield, is the commonest confusion: it is larger and more robust, with a warm brown to dark brown cap lacking any grey-green cast, and it does not develop blue-green tints at the stem base. Pluteus cinereofuscus and Pluteus podospileus are also small and greyish, but the former is a duller mouse-grey without green tones and the latter has a dark brown, velvety-granular cap centre with contrasting dark fibrils on the stem.

Entoloma species also have pink spore prints, but their gills are attached to the stem rather than free, and they typically grow from soil rather than wood. Volvariella species share free gills and pink spores but always have a membranous sac-like volva at the stem base, which Pluteus never has.