Birch Mazegill, Gilled Polypore

Description

Birch mazegill is a leathery, fan-shaped or bracket-shaped fungus growing on wood. The fruiting bodies are 2–8 cm wide, felty-hairy, concentrically furrowed, usually dirty white, grey, tan or straw-yellow; sometimes they turn green from algae. They grow in clusters, overlapping like roof tiles one above another. The underside consists of radiating, pale gills joined at the base.

It is common throughout Poland, except in the higher mountains. It grows on trunks, stumps and dead wood of deciduous trees, especially birch, alder, beech and oak, also in parks, gardens and on wooden fences and small bridges. The fruiting bodies can be found from summer to autumn.

It is distinguished from similar bracket fungi, e.g. turkey tail and hairy bracket, by its underside: the mazegill has gills, while those bracket fungi have tubes with fine pores. The fungus is inedible because it is tough and leathery.

Identification features

Cap

Annual fruiting body, bracket-shaped or semicircular, 2–8 cm wide (up to 13 cm according to some descriptions), 0.3–1.5 cm thick; attached to the substrate laterally or centrally. Fruiting bodies usually grow in clusters, overlapping like roof tiles, or are fused at the sides or at the base. Surface uneven, felty-hairy, concentrically zoned and furrowed. Colour dirty white, straw-yellow, grey or tan; sometimes green from growing algae. Margin thin, even, of the same colour or ochre-brown.

Hymenophore (underside of the cap)

Gilled (a rare feature among polypores). The gills radiate from the base, mostly smooth, sometimes torn; there are 12–15 per 1 cm of the fruiting body margin, exceptionally up to 17. They are joined by anastomoses at the base. Colour from white through pale grey to pale nut-brown.

Stem

No true stipe: the fruiting body is attached to the substrate laterally or centrally.

Flesh

Up to 1 cm thick, leathery, white or light brown. Taste and smell indistinct. The flesh should not be tasted.

Spore print and spores

Spore print white. Spores colourless, smooth, cylindrical with a pointed base, curved comma-like, 4.5–6.5 × 2–3 µm.

Habitat and distribution

Ecology. Saprotroph, rarely a parasite of weakened or damaged trees; causes white rot of wood. Grows on trunks and stumps of dead trees, rarely on living ones, and also on timber in use (fences, small bridges). Recorded on birch, alder, beech and oak.

Distribution. Common throughout Poland except higher mountain elevations: in deciduous and mixed forests, thickets, parks and gardens. Widespread in the temperate zone of the Northern Hemisphere. Not legally protected in Poland.

Fruiting. No clear data; fruiting bodies are annual, found from summer to autumn, and leathery, dried specimens persist longer.

What can it be confused with?

• Trametes versicolor (turkey tail) — Very similar on the upper surface, but has tubes with fine pores underneath rather than gills.
• Trametes hirsuta (hairy bracket) — Similar appearance of the upper surface; the hymenophore is porous (tubes with fine pores), not gilled.

Never rely on a single feature. If you are not sure — do not pick it; show the mushroom to a qualified mushroom expert.

Interesting facts

• Linnaeus described the species in 1753 as Agaricus betulinus; it has about 90 scientific synonyms.
• It is a gilled member of the order Polyporales, which consists mainly of tube-bearing fungi, so it is confused with bracket fungi with pores only at first glance.
• In 1955 the German scientist Lohwag showed that the species can be cultivated on an agar medium with beech sawdust added.
• It causes white rot of wood; timber in use is protected against it by impregnation with fungicides.