Giant polyporeMeripilus giganteus

The giant polypore (Meripilus giganteus), also called the black-staining or blackening polypore, is one of the biggest fungi in Europe and one of the most familiar in parks. It forms a huge rosette of dozens of brown, fan-shaped caps rising from a shared base at the foot of an old beech or oak, or sometimes straight out of the grass above its roots. Each cap is 10 to 30 cm wide, and the whole cluster is usually 50 to 80 cm across, sometimes more than a metre.

How do you identify it? Touch the pores on the underside: within a short time the spot turns brown and then black. Old and damaged caps darken too, until much of the cluster looks blackened. None of its lookalikes stains black like this, which makes it the most reliable test.

Is giant polypore edible? Opinions differ. Young, soft cap edges are eaten after slow, thorough cooking, and some foragers rate them well. Older fruit bodies are tough, fibrous and sour. Several sources warn that even young specimens upset some people's stomachs. Older guides, including Ukrainian ones, list it as inedible. No toxin has been found and we found no reports of serious poisoning. Because it grows at ground level in parks, think about dogs and lawn treatments before picking it there. Extracts have only been studied in the lab, so there's no evidence that it treats anything.

Giant polypore vs hen of the woods and chicken of the woods. Hen of the woods (Grifola frondosa) also forms a large rosette at the base of trees, usually oaks, but its fronds are smaller, 4 to 10 cm, and much thinner, greyer brown, and its pores don't blacken. It's also less common, so a big brown rosette by a park beech is far more likely to be a giant polypore. Chicken of the woods is bright yellow to orange, with yellow pores that don't blacken, though old, faded specimens are the ones people mix up. Umbrella polypore is made up of many small, pale, stalked caps on a branched base.

Where does it grow? Look at the base of beeches, less often oaks, limes, planes and other broadleaved trees, in parks, along streets and in old woodland. It fruits from summer to late autumn, mostly from late summer to autumn, and the fruit bodies soon collapse into a black, slimy mass after frosts.

What does it mean for the tree? The giant polypore is a parasite of the roots, causing white rot that starts in the deep roots under the trunk. By the time fruit bodies appear, those roots are often badly decayed, yet many trees stay standing for years, depending on how they respond. If it appears beside a tree in your garden or street, ask a qualified arborist to assess it, as some trees with it are at risk of falling. The fungus keeps fruiting on the stump and roots for several years after a tree dies or is felled.