Milk-white Toothed Polypore
Irpex lacteus
Also called irpex, milk-white irpex
A white resupinate fungus whose surface breaks from angular pores into flattened jagged teeth, usually with narrow hairy-topped caps along the margin.
Overview
Milk-white Toothed Polypore sits on the boundary between the pored and the toothed fungi. Young fertile surfaces are angular and pore-like, but the walls quickly tear apart into flattened, irregular spines two to five millimetres long, so a mature specimen reads as a toothed fungus rather than a polypore. The whole fruiting body is a clean milk-white when fresh, drying to a yellowish cream.
Most colonies are mainly resupinate, but the margin typically lifts into narrow, wavy caps a centimetre or two wide with a finely hairy white upper surface. Rows of these little brackets along a dead branch, each with a bristling white underside, are a good field signature.
The genus Irpex belongs to the Irpicaceae and I. lacteus is by far its commonest representative in temperate woodland, appearing on a very wide range of broadleaved wood across the Northern Hemisphere.
How to identify it
Fruiting body
Mostly resupinate, spreading in sheets along dead branches, with the outer margin usually reflexed into narrow caps 1–2 cm wide, often fused into tiered rows.
Upper surface of caps
White to cream, finely hairy or felted, sometimes with faint concentric zoning; frequently discoloured grey or green by algae on older specimens.
Fertile surface
Begins as angular pores but soon splits into flattened, ragged, tooth-like spines 2–5 mm long, irregular in size and often flattened and fused at the base. White to cream, drying yellowish-buff.
Flesh and spore print
Flesh is thin, white, tough and leathery, hardening on drying, with no colour change on cutting or bruising. Spore print white.
Where and when it grows
Grows on dead broadleaved wood of many kinds — fallen branches, logs, stumps and, very characteristically, standing dead branches and small trunks still held above ground. Beech, birch, willow, ash, maple and fruit trees are all regularly used.
Fruiting bodies can be found throughout the year, with fresh, brilliantly white growth mainly in autumn and early winter; older material persists in weathered, discoloured form. The species is widespread and common across Europe, North America and temperate Asia.
Ecological role
Irpex lacteus is a saprotroph causing an active white rot, degrading lignin strongly and reducing colonised branch wood to a pale, soft, fibrous state. It also colonises wounds and dying branches on living trees, spreading into wood that is already stressed.
It is often an early to mid-stage occupant of standing dead branches, fruiting while the wood is still off the ground, and the jagged teeth greatly increase the surface area available for spore production compared with a flat crust. Spores are dispersed by air currents from the pendent spines.
Similar species
Schizopora paradoxa is the nearest look-alike and shares white colour and a split fertile surface, but it remains flat without hairy reflexed caps and keeps recognisable pores near its margin.
Steccherinum ochraceum has similar flattened teeth but is distinctly ochre to salmon-pink rather than white. Trichaptum biforme forms comparable thin tiered caps on hardwood, but its fertile surface carries violet to lilac tones when fresh. Phlebia tremellosa is gelatinous with a netted rather than toothed surface.