Shaggy Mane Mushroom (Coprinus comatus)

Identification

Per the Missouri Department of Conservation field guide, shaggy mane has a white, shaggy, cylindrical cap, 1 to 2½ inches wide and 1½ to 6 inches tall, with flat white scales that turn brownish as it matures. The gills are narrow and crowded, starting white and turning black and inky from the margin inward. The stalk is tall, straight, smooth, and white, with a slightly bulbous base. It grows in large numbers along roadsides, lawns, and disturbed ground, fruiting September through October in Missouri (timing varies by region).

Why it must be eaten fast

Shaggy mane's defining trait is deliquescence: the cap and gills self-digest into a black, inky liquid as the mushroom ages, a normal part of its life cycle. Per the Missouri Department of Conservation, it's "considered choice edible but highly perishable", lasting only about 24 hours after picking. The standard advice is to pick only young, fresh specimens and cook immediately.

The lookalike that actually carries the alcohol reaction

The alcohol inky (Coprinopsis atramentaria) has a gray-brown, bell-shaped, radially lined cap, smaller and less cylindrical than shaggy mane's. Per the Missouri Department of Conservation, consuming it within about 3 days of alcohol causes body tingling, heart palpitations, headache, and nausea, from the compound coprine interfering with how the body metabolizes acetaldehyde. This reaction is specific to the alcohol inky and its coprine content, not to shaggy mane. A separate lookalike, the green-spored lepiota, is distinguished by its green spore print.

For the full comparison of shaggy mane against its dangerous lookalikes, see the Dangerous vs. Edible Mushrooms guide.