Winter Polypore

The Winter Polypore is a modest, long-stemmed little bracket fungus that belongs to the group of stalked polypores traditionally placed in Polyporus. Molecular work moved it, along with several relatives, into Lentinus, though the name Polyporus brumalis remains in wide circulation in field guides. The specific epithet refers directly to its habit of fruiting in the depths of the cold season.

In form it is a miniature version of the familiar stalked-polypore body plan: a small circular cap dimpled at the centre, a slender central stem, and a layer of white tubes on the underside that run a short way down the stem. The whole fruit body is tough and pliant rather than fleshy, and can withstand repeated freezing and thawing, which is precisely what allows it to occupy the winter niche.

Because few other agarics or polypores are producing fresh fruit bodies in midwinter in temperate woodland, a small stalked polypore found on a fallen stick in January is very likely to be this species. It is common and widespread across Europe, northern Asia and much of North America.

Cap

The cap is small, typically 2 to 8 cm across, convex at first then flattening and developing a shallow central depression or dimple. The colour is a subdued grey-brown, mouse-brown or greyish-ochre, sometimes almost blackish-brown in exposed specimens, and the surface is finely velvety or minutely hairy when young, becoming smoother and often slightly wrinkled with age. Young caps have an inrolled margin that may carry a very short fringe of fine hairs, but this is inconspicuous and quickly lost.

Pores

The pore surface is white to cream, ageing to pale buff or greyish. The pores are small and round to very slightly angular, about 2 to 4 per millimetre, and are clearly decurrent, running noticeably down the top of the stem. Tubes are shallow, only 1 to 3 mm deep.

Stipe

The stipe is central or nearly so, slender, 2 to 6 cm long and only 2 to 6 mm thick. It is grey-brown to pale brownish, finely velvety or minutely scurfy over its whole length, and importantly it is not sharply blackened at the base, though it may darken slightly where it enters the wood.

Flesh and spore print

The flesh is thin, white, and tough and leathery in texture, showing no colour change on cutting. Old fruit bodies dry to a hard, rigid disc that rehydrates in wet weather. The spore deposit is white.

This is a fungus of small dead hardwood debris. It fruits on fallen sticks, twigs, thin branches and slender logs of deciduous trees, particularly birch, beech, hazel, willow, alder and various fruit trees, and it will often colonise wood only a few centimetres in diameter. Because its substrate is small and quickly consumed, fruiting on any given stick tends to last only a season or two.

The season is the defining habitat feature. Fruit bodies appear from late autumn, persist and continue to develop through winter, and finish in early spring, so that the peak coincides with the coldest and wettest part of the year in temperate woodland. It is widespread throughout Europe, common across northern and temperate Asia, and well distributed in North America, generally in mixed and deciduous woodland, hedgerows, scrub and damp thickets.

Lentinus brumalis is a saprotroph causing a white rot in small-diameter deciduous wood. It specialises in the fine woody litter layer, the sticks and twigs that fall continuously from the canopy and would otherwise accumulate on the forest floor, and its decay softens and bleaches this material so that it fragments and mixes into the soil.

Its cold-season fruiting strategy reduces competition, both from the many polypores and agarics that fruit in autumn and from the invertebrates that graze on softer fruit bodies. The tough, low-water-content flesh survives frost, so a single fruit body can release spores intermittently over many weeks whenever conditions become mild and damp. Spores landing on freshly fallen sticks establish new colonies, continuing a rapid cycle of small-substrate decomposition.

The nearest relative and main source of confusion is the Spring Polypore, Lentinus arcularius. That species has distinctly larger, angular to hexagonal pores of roughly 1 to 2 per millimetre, a warmer yellow-brown to tan cap with small flattened scales, and a conspicuous fringe of coarse hairs around the cap margin that persists into maturity. It also fruits in spring and early summer rather than winter.

Neofavolus alveolaris has a bright orange to reddish-orange scaly cap when fresh, very large radially elongated hexagonal pores, and a short lateral or strongly off-centre stem. Picipes badius is much larger, with a smooth glossy chestnut cap, pores far finer than in the Winter Polypore, and a stem whose lower half is sharply black. Cerioporus varius has an ochre-tan cap and, again, a black-based stipe, which the Winter Polypore never shows.