Bondarzewia berkeleyi

Description
Bondarzewia berkeleyi, commonly known as Berkeley's polypore, or stump blossoms, is a species of polypore fungus in the family Russulaceae. It is a parasitic species that causes butt rot in oaks and other hardwood trees. A widespread fungus, it is found in Africa, Asia, Europe, and North America.

Elias Magnus Fries described the species as Polyporus berkeleyi in 1851. It was moved to the genus Bondarzewia in 1941.

The fan- or shelf-shaped caps grow in overlapping clumps from the bases of oak trees, each capable of growing to 25.5 cm (10 in) diameter. They are various shades of white to pale grey, cream, beige or yellow. The pore surface is white, as is the spore print. The round spores are 7–9 by 6–8 μm and have marked amyloid ridges. The tough white flesh can be up to 3 cm (1.2 in) thick and has a mild taste, which can be bitter in older specimens. The outer edges that cut easily with a knife are quite tender. Although Bondarzewia berkeleyi has been compared to eating shoe leather, some field guides list it as edible. It may be able to be used to strengthen other flavors in dishes, much like tofu. It can also reportedly be used as a meat substitute. Other field guides list it as inedible.

In China it has been recorded from Guangdong and Hunan provinces. The fruit bodies appear over July to October in the United States. A survey of host trees in North Carolina found that it almost always grew on oaks, being recorded from the white oak (Quercus alba), scarlet oak (Q. coccinea),  southern red oak (Q. falcata),  chestnut oak (Q. prinus) and eastern black oak (Q. velutina), as well as bird cherry (Prunus pensylvanica).

Ecology
Bondarzewia berkeleyi is a parasitic fungus that primarily affects hardwood trees, particularly oaks (Quercus spp.). It causes a white stringy rot in the roots and heartwood of the lower trunk, typically not extending more than 3–5 feet upwards. The decay is mainly restricted to the heartwood, and external symptoms might include excessive tapering or flaring at the base of the trunk, cracks, seams, and sap flow. The fungus is known for its rapid growth rate compared to other wood-rotting fungi common on oaks.

While primarily a parasite, B. berkeleyi can also act as a saprophyte, thriving on dead hardwood trees or stumps. The fruiting bodies, which are the visible part of the fungus, typically appear at the base of infected trees in summer and fall.

The distribution of B. berkeleyi is widespread, occurring in North America east of the Great Plains, Europe, Asia, and Africa. While its primary host is oak, it has also been observed on other hardwood species such as maple.

Edibility
Bondarzewia berkeleyi is considered edible when young and tender, but its palatability decreases with age as the flesh becomes tough and bitter. Some sources compare the texture to shoe leather when older, while others suggest that the softer outer edges of young specimens can be consumed.

Preparation methods often involve parboiling or blanching to remove bitterness, followed by slicing and incorporating into stir-fries or other dishes. It's important to note that there are conflicting opinions regarding the edibility of B. berkeleyi. While some field guides list it as edible, others label it as inedible or caution against consumption due to its potential for causing gastrointestinal upset or allergic reactions in some individuals.

If you choose to consume B. berkeleyi, it's crucial to properly identify the mushroom, harvest only young specimens, and thoroughly cook them before consumption. Consulting with a local mycological expert or foraging guide is recommended before consuming any wild mushrooms.