Grifola frondosa
Grifola frondosa is a polypore mushroom that grows in clusters at the base of trees, particularly oaks.  The mushroom is commonly known among English speakers as hen-of-the-woods, ram's head and sheep's head.  It is typically found in late summer to early autumn. In the United States' supplement market, as well as in Asian grocery stores, the mushroom is known by its Japanese name maitake (舞茸, "dancing mushroom"). Throughout Italian American communities in the northeastern United States, it is commonly known as the signorina mushroom.
G. frondosa should not be confused with Laetiporus sulphureus, another edible bracket fungus that is commonly called chicken of the woods or "sulphur shelf". It is native to China, the northeastern part of Japan and North America.

Description
Like the sulphur shelf mushroom, G. frondosa is a perennial fungus that often grows in the same place for a number of years in succession. It occurs most prolifically in the northeastern regions of the United States, but has been found as far west as Idaho.

G. frondosa  grows from an underground tuber-like structure known as a sclerotium, about the size of a potato. The fruiting body, occurring as large as 100 cm, is a cluster consisting of multiple grayish-brown caps which are often curled or spoon-shaped, with wavy margins and 2–7 cm broad. The undersurface of each cap bears about one to three pores per millimeter, with the tubes rarely deeper than 3 mm. The milky-white stipe (stalk) has a branchy structure and becomes tough as the mushroom matures.

In Japan, the maitake can grow to more than , earning this giant mushroom the title "king of mushrooms".

Uses
Maitake has been consumed over centuries in China and Japan where it is one of the major culinary mushrooms. The mushroom is used in many Japanese dishes, such as nabemono.

Research
Although under laboratory and preliminary clinical research for many years, particularly for the possible biological effects of its polysaccharides, there are no completed, high-quality clinical studies, no approved drugs, and no applications in modern clinical practice for Grifola frondosa, as of 2019.