Alder Scalycap

Pholiota alnicola is a wood-rotting agaric of damp woodland, named for its strong association with alder. Despite the English name it is one of the least scaly members of the genus: the cap is essentially smooth, and the scaliness suggested by the name is limited to the sparse fibrillose veil remnants on the stipe and occasional flecks near the cap margin.

The species forms part of a variable complex, with taxa such as P. salicicola on willow and P. flavida on conifer debris treated by some authors as varieties or close relatives. All share the same basic look: clear sulphur to lemon-yellow caps in dense, upright clusters, slender curved stipes fused at the base, and gills that mature to a dull cinnamon or clay-brown.

In the field it is one of the brightest autumn sights of alder carr and wet birch woodland, where whole ranks of yellow caps can line a fallen trunk or crown a submerged stump at the edge of a stream.

Cap

Generally 3-8 cm across, convex to broadly convex and finally almost flat, often with a slightly incurved margin. The colour is a clean sulphur or lemon-yellow, frequently warming to tawny or ochre at the centre in mature specimens. The surface is smooth to faintly fibrillose and slightly viscid when moist, drying silky; conspicuous scales are absent, although fine pale veil fragments may fringe the margin when young.

Gills

Adnate, crowded and fairly narrow, pale yellow at first and darkening through ochre-yellow to a dull cinnamon or clay-brown as spores ripen. The gill edge tends to stay paler than the faces.

Stipe

Slender, 4-10 cm long and 5-10 mm thick, usually curved or sinuous because the caps grow upwards from a horizontal or angled substrate, and joined to its neighbours at a common fused base. It is bright yellow in the upper part and darkens progressively to rust or tawny brown towards the base, with scattered fibrillose veil fibres and a faint ring zone that may be dusted brown with spores.

Flesh & spore print

The flesh is pale yellow, thin and firm, unchanging when cut. Fresh material has a distinct sweetish, slightly aromatic or fruity odour, which is a helpful supporting character. The spore print is clay-brown to dull rust-brown, and the spores are smooth with a germ pore.

This is a fungus of wet woodland and waterside scrub. It fruits in dense tufts on the stumps, cut ends, fallen trunks and exposed roots of alder above all, and also on birch, willow and occasionally other broadleaves. Typical sites are alder carr, stream and ditch banks, pond margins, damp woodland flushes and boggy ground where alder forms thickets.

The main season is autumn, with clusters appearing from early September onwards and continuing until hard frosts. Because the fungus exploits submerged and buried roots, tufts sometimes appear to spring from wet ground beside a tree. It is widespread across temperate and northern Europe and occurs in comparable habitats across northern Asia and North America.

Pholiota alnicola is a saprotroph, and to a limited extent a wound coloniser, of alder and other wetland broadleaves. It causes a white rot, degrading both lignin and cellulose so that infected stumps become pale, soft and fibrous before crumbling away. Alder is a short-lived, fast-growing pioneer that regenerates readily by coppicing, so cut stools and dead stems are abundant in carr woodland and provide a plentiful substrate.

By breaking down this waterlogged deadwood the fungus helps recycle nutrients in a habitat where decomposition is otherwise slowed by anaerobic conditions. The nitrogen-rich tissue of alder, itself supported by nitrogen-fixing root bacteria, makes its wood a comparatively rich resource, and the resulting decayed material becomes a key component of the organic soils of streamside woodland.

Hypholoma fasciculare, the Sulphur Tuft, grows in equally dense yellow clusters on stumps but its gills turn distinctly greenish-yellow before becoming purplish, and its spore print is purple-brown rather than clay-brown. Pholiota flammans is a brighter golden-yellow and is unmistakably shaggy, with dry cottony upright scales on both cap and stipe, and it grows on conifer wood.

Pholiota gummosa is paler, more greenish-buff or straw-coloured, with a stickier cap and a stouter stipe, and typically fruits on buried broadleaf debris in soil rather than on visible stumps. Kuehneromyces mutabilis shares the tufted habit but has a two-tone hygrophanous tan cap and a scaly stipe below a distinct ring, and lacks the clean lemon-yellow colouring.