Birch Polypore

not listed

Very common in eastern Minnesota

June through fall, but present year round

Deciduous woodlands. Birch.

Birch Polypore is a very common, easily recognized bracket fungus. It occurs in Europe, Asia, and North America. In the United States it occurs from Maine to North Carolina, west to Kansas, and in the northwest. It is very common in the woodlands of eastern Minnesota. It grows alone, in groups, or in columns exclusively on birch, usually on dead trees and logs, sometimes on living trees. It obtains its nutrients from dead wood (saprobic). It also attacks weakened live trees, killing them and then feeding on the dead wood (necrotrophic). It is annual but the cap persists through the winter.

The cap is kidney-shaped to almost round in outline, 2″ to 10″ (5 to 25 cm) wide, and ¾″ to 2⅜″ (2 to 6 cm) thick. It is white, smooth, and hairless when young. The upper surface is covered with a thin skin. As it ages, the skin becomes pale grayish-brown, cracks, and often breaks away in small patches. The margin is thick, rounded, and rolled under, creating a “curb” around the pore surface on the underside.

The pore surface is white at first, turning yellowish-brown as it ages. It is recessed, with the curb-like margin extending below it. The pores are small, with 2 to 4 pores per millimeter. The bracket is annual so there is only one layer of pores.

There is often no stalk. When present, the stalk is thick, up to 2⅜″ (6 cm) long, and attached to the side or top of the cap.

The flesh is white, thick, and corky. It is edible when young but it is tough and it may be bitter.

The spore print is white.

Sources: 4, 7, 24, 26, 29, 30, 77.

Taxonomy
This species was originally classified in 1788 as Boletus betulinus. In 1881 it was transferred to the genus Piptoporus. Based on molecular phylogenetic studies published in 2013 and 2016, it was transferred to the genus Fomitopsis in 2017.

Ötzi
Ötzi, the Tyrolean Ice Man who was frozen 5,000 years ago and thawed in 1991, carried two species of fungus with him: true tinder polypore and birch polypore. The former was part of a fire lighting kit, the latter was probably used for medicinal purposes.

Location: Cass County