One of our most striking and otherworldly forest dwellers, the so-called lion's mane grows off injured or recently fallen hardwoods, mostly oak. You can easily distiguish it by its thin tendrils, prodruding from a white rubbery center. It looks a bit like a sea anemone crossed with coral. The flesh is white to off-white, slightly translucent and rubbery. The base can sometimes be very strong and difficult to remove from the host tree without a sharp knife.
H. erinaceus is edible and delicious when young, a similar texture to octopus or squid. It has a subtle citrus-floral flavor, and a musky delicate smell. I recommend cooking it with other subtle flavors. It pairs well with shellfish such as scallops or mollusks in light citrus based sauces, perhaps sautéed with light pearl sauce and shiitake, or chilled in a salad with sesame oil and seaweed.
The specimen pictured at the top is a bit of a puzzle. It was young and fresh, with delicious fragrance and flavor, but had a slightly pinkinsh-buff exterior rather than pure white. The specimen below was too old to eat, and had actually started to deliquesce slightly at the top. By the time H. erinaceus starts turning yellow-tan like this one, it has developed an unpleasant sour taste. Eat it young if you can find it, and enjoy its firm chewiness and subtle sweetness.