Black-staining Polypore

Description

The black-staining polypore is one of the largest tree fungi: a huge clump of overlapping, fan-shaped caps in brown, concentrically zoned shades, with a pale cream margin. The whole may be from several tens of centimetres to over a metre across and weigh a dozen or even several dozen kilograms.

It grows in autumn at the base of broadleaf trees, most often beeches and oaks, often in parks and by roads. The most reliable feature is the underside with very fine pores, which turns brown and then black when touched or damaged; the flesh turns black in the same way.

It can be confused with the hen of the woods, which has paler, smaller caps and does not turn black.

Identification features

Cap

Fruiting body annual, large, 30–150 cm across, rarely up to 250 cm (descriptions give different ranges), made of many overlapping, fan-shaped or semicircular caps growing from a common base, sometimes on short stems. Individual caps 10–50 cm wide and 1–5 cm thick. Surface at first yellow-brown, later brownish, chestnut, distinctly concentrically zoned, covered with fine scales. Margin paler, cream, rounded, wavy with age.

Hymenophore (underside of the cap)

Tubes short, whitish, staining brown when damaged and then turning black. Pores very fine, circular, about 0.3 mm (3–6 pores per mm).

Stem

No distinct stem; the caps grow from a common base, sometimes on short stems.

Flesh

White, bast-like (tough and stringy), fibrous, turning black in section, strongly mushroomy smell, sourish or slightly acidic taste; flesh very thick. Never taste the flesh of unknown mushrooms.

Spore print and spores

Spore print colour: no data. Spores smooth, colourless, ovoid to circular (6–6.5 × 5.5–6 µm, non-amyloid).

Habitat and distribution

Ecology. A tree-dwelling fungus, causing white rot. Grows at the base of various broadleaf trees (especially beech and oak), exceptionally conifers, usually near dead stumps, less often as a parasite of living trees; infection often through a dead taproot, decay mainly in the roots. It readily grows in parks and by roads (hence the name “park fungus”); fruiting bodies may grow somewhat away from the trunk, from the roots. It can cause trees to topple through brittle breakage of rotten lateral roots.

Distribution. Europe, Asia, North Africa, New Zealand; according to some descriptions the related M. sumstinei occurs in North America, not this species (descriptions differ). Many sites in Poland; it was protected until October 2014, now without legal protection. In Hamburg it is the most common wood-decay fungus on street and park trees.

Fruiting. Autumn; after the first frosts the fruiting body dissolves into a slimy black mass. Exact months — no data.

What can it be confused with?

• Grifola frondosa (hen of the woods) — Occurs almost exclusively on oaks, has smaller and narrower caps, more greyish, larger pores; the hymenophore does not turn black when damaged.
• Bondarzewia mesenterica (mountain bondarzewia) — Grows at the base of firs; has large, angular, uneven pores, and the flesh does not turn black in section.

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

• Single fruiting bodies can weigh several dozen kilograms; the heaviest known specimen reached 90 kg.
• After the first frosts the fruiting body dissolves into a black, slimy mass.
• In Hamburg it was the most common wood-decay fungus on street and park trees.
• Until October 2014 the species was protected in Poland.