Willow Bracket

The Willow Bracket is a perennial hoof fungus that can persist on a single tree for decades, adding a new layer of tubes each year beneath the old. Its exterior weathers to a hard, grey to black, concentrically furrowed and radially cracked crust that often carries algae or moss, so that an old specimen looks more like a lump of charcoal or weathered rock than a fungus.

It belongs to Phellinus in the Hymenochaetaceae, the family whose members share rusty brown flesh and minute pores. In practice Phellinus igniarius as usually understood is a complex of closely related taxa separated largely by tree preference and subtle shape differences, including forms on aspen, alder and birch. All share the same essential structure: a woody perennial fruit body with stacked annual tube layers and a bright rusty brown context.

Cutting one in half is the most instructive way to understand it. The section shows a thin dark crust, a hard rusty brown context beneath, and then a series of distinct tube strata piled one on another, each representing a year of growth, with only the lowest layer actively producing spores.

Fruit body

The bracket is hoof-shaped to cushion-shaped or sometimes rather flattened, 5 to 25 cm wide and up to 15 cm thick, broadly and firmly attached to the trunk. It is extremely hard and woody, quite unyielding to a fingernail, and grows a little larger each year. Fruit bodies commonly occur singly but several may appear along one trunk.

Upper surface

The top is dull grey to grey-black or nearly black, hard and crusted, marked with strong concentric furrows and ridges and typically split by numerous radial cracks. Older parts are often colonised by algae, giving a greenish cast, or by mosses and lichens. The margin is thick, blunt and rounded, and is usually paler, a narrow band of rusty brown to greyish-brown marking the current season of growth.

Pores

The pore surface is cinnamon to rusty brown when fresh, dulling to greyish-brown with age, and is often slightly paler at the actively growing edge. Pores are minute, roughly 4 to 6 per millimetre, so the surface looks matt and almost smooth from a distance. Sectioning reveals distinct stacked annual tube layers, often separated by thin bands of context.

Flesh and spore print

The context is hard, woody and rusty brown to yellow-brown, sometimes with faint concentric zoning and often with small pale flecks. There is no colour change on cutting beyond the natural darkening of exposed tissue. The spore deposit is white.

The Willow Bracket grows on living broadleaved trees, and as its English name suggests it is most strongly associated with willows of many species. It is also frequent on birch, alder, poplar and aspen, and is recorded on beech, hawthorn, apple and other broadleaves. It fruits from wounds, broken branch stubs and old bark injuries on the trunk or major limbs, and often reappears at the same point for many years.

Because the fruit body is perennial it is present all year, though the fresh growing margin is most obvious in summer and autumn and spore release is concentrated from spring through autumn. The species complex is widespread across the whole north temperate zone, common throughout Europe, northern and temperate Asia and North America, and reaches into the boreal zone wherever willow and birch grow. Typical habitats include riverside willow carr, wet woodland, hedgerows, birch woods and upland scrub.

Phellinus igniarius is a parasite of living broadleaved trees, causing a white rot of the heartwood. The mycelium enters through wounds and spreads within the central wood of the trunk, breaking down lignin and cellulose so that the affected core becomes pale, soft and eventually spongy or hollow while the outer living sapwood continues to function. Infected trees may live and grow for many years with substantial internal decay.

The perennial fruit body represents a long-term investment: rather than rebuilding each season, the fungus adds a new tube layer under the old and maintains a hard weatherproof crust above, which lets it release spores over decades from one established colony. Ecologically the hollowing it produces is important habitat, since decayed willow and birch trunks provide nest sites for hole-nesting birds and roosts for bats, while the softened wood supports specialist invertebrates. After the tree dies the fungus continues as a saprotroph in the standing snag.

Fomes fomentarius, the Hoof Fungus, occupies similar trunks on birch and beech but has a smoother, more evenly grey to grey-brown crust that is concentrically banded but not deeply cracked, a pale grey-brown to buff pore surface rather than rusty, and softer, pale brown, felty context. Fomitiporia robusta is very similar in structure but grows on oak, is more cushion-shaped than hoof-shaped, and has a less deeply cracked surface.

Phellinus tremulae is confined mainly to aspen and typically forms a more sharply triangular bracket in section. Ganoderma applanatum is flatter and shelf-like with a thin dull brown crust, and its white pore surface bruises brown instantly when scratched, a reaction absent here. Fuscoporia gilva is a thin annual shelf with a mustard-yellow top, not a hard perennial hoof.