Birch Mazegill

The Birch Mazegill is the classic demonstration that gills and pores are not reliable guides to relationship. From above it is indistinguishable from a Trametes — thin, hairy, concentrically zoned, broadly attached to dead wood — but turning it over reveals a set of thick, radiating gill plates rather than a pore surface. Molecular work has confirmed what the upper surface suggests: this is a polypore relative that has independently evolved a gill-like hymenophore, and it is now often treated as Trametes betulina.

The gills are the whole point of the species for identification purposes. They are thick, well spaced, blunt-edged and frequently forked or joined by cross-plates near the base, giving a partly maze-like appearance in older specimens. They stay pale — whitish, cream or greyish buff — throughout.

Despite the name, birch is only its most typical host. It is a widespread hardwood decomposer found across the temperate northern hemisphere and into the tropics.

Cap

Brackets are 3-12 cm across and 0.5-2 cm thick, semicircular to fan-shaped, broadly attached and stalkless, often overlapping in tiers or fused laterally. The upper surface is densely hairy to finely velvety, marked with concentric zones in whitish, cream, tan, grey and greyish brown, and is very frequently greened by algae in older specimens. The margin is thin and often paler.

Gills

The underside carries true gill plates radiating from the attachment to the margin. They are thick, tough, blunt-edged, spaced roughly 1-2 mm apart, and often fork or are joined by short cross-walls near the base so that the pattern becomes partly labyrinthine. They are whitish to cream when fresh, ageing pale greyish buff or dull tan, and never develop a purple, red or rust cast.

Flesh & spore print

The context is white, thin, tough and leathery, drying hard and remaining pale in section. There is no stipe, no ring and no volva. The spore print is white, from smooth cylindrical spores.

It fruits on dead hardwood: birch above all, but also beech, oak, willow, alder, hazel, poplar and fruit trees. Fallen trunks, large branches, standing dead stems and stumps are all colonised, especially where the bark has been lost. It is most often seen in open woodland, hedgerows and log piles rather than deep shade.

The species is widely distributed across Europe, Asia, North America and beyond, extending from boreal birch forest into warm temperate regions. New brackets develop from summer through autumn, and the tough dried fruit bodies remain on the wood through winter and often into a second year.

The Birch Mazegill is a saprotrophic white-rot fungus. It breaks down lignin as well as cellulose, leaving the wood pale, soft and stringy, and it typically colonises recently dead branches and trunks in the early to middle stages of decay.

The gill-like hymenophore is an evolutionary convergence: gills provide a large spore-bearing surface for the same reason tubes do, and several unrelated polypore lineages have arrived at the same solution. Because the plates are thick and rigid rather than soft, they survive drying and continue producing spores when conditions turn damp again. The brackets themselves are a persistent deadwood micro-habitat used by beetles and other invertebrates through winter.

Gloeophyllum sepiarium, the Conifer Mazegill, also has gill-like plates but they are ochre to rust-brown rather than whitish, the upper surface is warm rusty brown with a bright orange growing edge, and it grows on conifer wood and worked softwood timber. Daedaleopsis confragosa has a maze of elongated pores rather than clean radiating gills, browner reddish zoning above, and a pore surface that flushes pink-red where bruised.

Trametes hirsuta and Trametes versicolor look near-identical from above but show round pores beneath. Daedalea quercina has a much thicker, corky body with a deeply labyrinthine, thick-walled underside and grows on oak. Small Panellus and Plicaturopsis species have thin, soft, non-persistent flesh rather than tough leathery tissue.