Shaggy Scalycap

Pholiota squarrosa is the archetype of its genus: a shaggy, dry, yellow-brown mushroom that fruits in tight bundles at the base of trees, its cap and stem covered in coarse scales that stand out and curl back like roof tiles lifted by the wind. The specific epithet squarrosa refers exactly to that character, describing scales that are raised and recurved rather than flat.

Pholiota belongs to the family Strophariaceae, and its members share rusty brown to cinnamon spore prints, attached gills that age from pale yellow to rust, and a partial veil that leaves a ring or ring zone. Species within the genus are split largely on whether the cap surface is dry or viscid beneath the scales, on the scale form, and on host preference. P. squarrosa is the dry-capped species with the most strongly recurved scales.

Unlike many wood-decay fungi it frequently attacks living trees at the root collar, so its bundles are often found hugging the trunk of a standing, apparently healthy tree rather than on a stump. That habit, combined with the rough scaly texture, makes it one of the easier autumn wood fungi to name at a glance.

Cap

The cap is 3-12 cm across, at first almost spherical then convex and finally broadly flattened, sometimes with a low umbo. The ground colour is straw yellow to pale ochre or greenish yellow, and the whole surface is dry, never sticky, and densely covered with coarse, upturned, recurved scales in tawny brown to rusty brown. The scales are concentrically arranged and are largest and most crowded towards the centre. The margin is inrolled when young and often carries hanging veil fragments.

Gills

The gills are adnate, sometimes with a short decurrent tooth, and are crowded and narrow. They start pale straw yellow, pass through a distinctly greenish or olive-yellow phase in many collections, and finally turn dull rusty brown as the spores mature.

Stipe

The stipe is 5-12 cm long and 1-1.5 cm thick, usually curved because the clumps crowd one another, firm and fibrous, and often fused with neighbours at the base. Above the ring zone it is smooth and pale yellow; below it is covered with the same shaggy recurved brown scales as the cap. The partial veil leaves a distinct but ragged fibrillose ring or flaring ring zone, above which the stem is clean.

Flesh and spore print

The flesh is pale yellow, firm, and browner in the stem base. The odour is characteristic and useful, often described as garlicky, radish-like, or resembling cut onion, and it becomes stronger in older specimens. The spore print is rusty brown to dull cinnamon brown.

This species fruits in dense clusters at the base of standing trunks, on exposed roots at the root collar, and on stumps and fallen trunks. It has a broad host range covering both broadleaf and coniferous trees, with beech, ash, birch, sycamore, apple and other fruit trees, and rowan among the common hardwood hosts, and spruce and other conifers used regularly in northern and upland areas. It is a familiar fungus of parkland, gardens, orchards, hedgerows, and mixed woodland.

Fruiting runs from late summer through autumn, peaking in cool damp weather and continuing until hard frost. Distribution is broad across temperate Europe, northern Asia, and North America, and it is one of the more frequently encountered Pholiota species throughout that range.

Pholiota squarrosa is both a parasite and a saprotroph. It commonly begins as a weak parasite entering a living tree through root or basal wounds, and it then causes a butt rot and root rot that hollows the base of the trunk, weakening the anchorage and predisposing the tree to windthrow. After the tree dies it continues on the same wood as a saprotroph, so a colony can persist in one place for many years, fruiting from the same root plate season after season.

The decay it produces is a white rot, with lignin and cellulose both broken down and the affected wood left pale and fibrous. In ecological terms it is one of the agents that create standing hollow trunks and basal cavities, features which are valuable roosting and nesting habitat. Fruiting bodies arise from a common mycelial mass, which is why the stems are crowded, curved, and often joined at the base.

Pholiota squarrosoides is the closest relative and is separated by touch and colour: its cap is sticky or tacky beneath the scales in damp weather rather than completely dry, the ground colour is whitish to pale cream rather than yellow, and its gills stay white far longer before turning rust. The Golden Scalycap, Pholiota aurivella, has a markedly viscid, glossy golden-orange cap with flat appressed scales that often wash off, and it typically fruits high on trunks in wounds and branch scars rather than at the base.

The Spectacular Rustgill, Gymnopilus junonius, forms similar large orange clusters at tree bases and also drops rusty spores, but its cap is smooth to finely fibrillose rather than shaggily scaly and it carries a more definite membranous ring. Honey Fungus, Armillaria species, shares the clustered basal habit and can look scaly, but its gills are whitish and decurrent, its spore print is white, and black bootlace rhizomorphs are usually present in the bark or soil nearby.