Chaga or Artist's bracket

Chaga has no cap. What you see on the birch is a growth 10–30 cm across, occasionally up to 40 cm, or sometimes a narrow strip up to a metre long running along a crack in the trunk. It's irregular and knobbly, bursts out through the bark and sits firmly on the tree with a broad base.

The surface is black, matt, dry and very hard, broken by deep cracks into small facets, like charcoal or burnt wood. The black colour comes from the pigment melanin. Around the edges, where the growth pulls away from the bark, the rusty brown interior often shows through.

The fruiting body is 10-50 cm across (sometimes up to 70 cm), flat and spreading, fan-shaped or semicircular, and attached sideways to the substrate (the trunk of a broadleaf tree), with no stem. The upper surface is hard and corky, with clear concentric zones of annual growth, one zone for each year of life. It's brownish grey or olive grey, and mature brackets carry a rusty coating of spores. The margin is whitish when young and darkens with age.

The growth has no underside with pores or gills: it's a sterile mass of fungal threads and produces no spores.

The true fruiting body appears once the tree, or part of it, has died, often on the opposite side of the trunk. It spreads under the bark as a thin crust 0.5–1 m long, whitish at first and then brown, made of tubes. Eventually the bark splits open and exposes a brown layer of pores. It is rarely seen.

Underneath are tiny white pores (4-6 pores/mm). The surface is whitish cream and darkens distinctly when pressed or scratched, a key diagnostic feature. The spore print is rusty brown and often shows as a rusty coating on the trunk around the bracket.

There's no stem. The growth comes straight out of the trunk, usually at an old wound or broken branch, and is fused to the wood so firmly that only an axe will remove it.

No stem. The fruiting body is attached to the substrate by its side edge.

Inside, chaga is dense, corky and woody. The colour is rusty brown, turning yellowish orange towards the wood, often with pale streaks. This bright interior is what sets chaga apart from other black growths on birch. It doesn't change colour when broken.

The flesh is very tough, corky-fibrous and brownish chestnut, leathery and hard as wood. It's no use in cooking. The smell is faintly woody.

Chaga has no distinctive smell, and descriptions of the species don't mention one. Identify it by appearance instead: a black, cracked surface and a rusty yellow interior on a living birch.

Faintly woody, nothing distinctive.