Willow Bracket

The bracket measures 5–20 centimetres (2–8 in) in diameter, but in rare cases may be 40 cm wide. The thickness of the bracket varies from 2–12 cm (1–4+1⁄2 in), to 20 cm in exceptional cases. These conks are among the longest persisting fungal fruit bodies, displaying up to eighty annual growth rings. The fungus has small, grayish brown pores, about 4–6 per square millimetre. Its tubes have a length of about 2–7 mm (1⁄8–1⁄4 in). Each year, the fungus forms a new layer of tubes superimposed on the old layers. Unreleased old spores often find themselves sealed in by later growth that clog the tubes and they appear in cross section as brown spots. The brown flesh is 10–20 cm (4–8 in) thick and becomes harder with age and dryness, softer with humidity. The smell of the fruit body has a pronounced mushroom character, the flavor of the meat is bitter. Upon contact with potassium hydroxide, the flesh is dyed black. The spores form a whitish cast.

Similar species. Similar species include P. arctostaphyli, P. pomaceoides, P. tremulae, Fulvifomes robiniae, and members of Fomitiporia.

The species is a polypore, with pores on the underside that bear basidiospores. The species causes a white rot that leads to the tree to decay. Woodpeckers are known to favour its site as a good place to excavate a nesting chamber since the wood will be soft and weaker around its location.

The species is considered to be inedible, being woodlike. There is some evidence that it may have potential medicinal uses. A 2014 study in mice suggests an extract of the mushroom fruit body may have a high therapeutic potential for ameliorating multiple sclerosis progression. It was prized as kindling material. In Alaska, it is burnt by locals, and the ash (punk ash) is mixed with chewing tobacco to enhance the effect of the nicotine.