Mushrooms can grow nearly anyplace that is rich enough in nutrients, moist enough and shaded adequately. They often grow on animal droppings, such as horse and cow dung. The fungi that grow on cow manure are not necessarily the same species as those that grow on horse manure, however. Identifying fungus that grows on horse manure takes some careful observation and a keen eye. Thankfully, only eight species of fungus commonly grow on horse manure.
Look for a bell-shaped, white or cream-colored mushroom no taller than 2 inches with a chalk-white "mealy" covering on its cap. This fungus growing on horse manure is the Coprinus niveus, also called Schneeweisser Tintling or Snowy Inkcap. You'll find this odorless mushroom growing on horse manure in summer through autumn.
Identify Psilocybe cubensis or Singer Cap by its white bell-shaped to broadly conical cap that is yellowish to brownish in the center. This fungus grows on horse manure nearly year round and reaches a height of 2 to 6 inches. This mushroom's flesh turns bluish when bruised or cut.
Identify Peziza vesiculosa, also called Blistered Cup, by its cup-shaped and yellow, gray to beige cap that grow from 1 to 3½ inches wide. The 2- to 6-inch tall mushroom grows year round on horse manure.
Look for a gray to beige-colored mushroom growing on horse manure in the autumn. This fungus is the tiny Poronia punctata, also known as Nail Fungus, and it grows no larger than 2 inches tall with a long, cylindrical, black stalk.
Recognize the Psilocybe merdaria, or Dung-Trauschling or Stropharia merdaria, by its slimy or sticky brown flesh and 1- to 2-inch-wide conical cap. The mushroom grows on horse manure in late summer to autumn, growing to only 2 inches tall at most with purplish-brown gills. Its stem is usually whitish or light yellow with a base coated in white down.
Identify Panaeolus campanulatus, also called Bell-Shaped Mottlegill or Glockendungerling, by spotting its hemispherical, conical, 1- to 1½-inch cap that is pale beige around the edges and reddish-brown in the center. The stem is noticeably longer than the cap and is gray or gray-brown. This 2-inch-tall mushroom grows on horse dung in late summer to autumn.
Look for a 2- to 6-inch tall fungus growing on horse manure in late summer to fall with a long stem and conical or convex cap that is ¾ inch to 3 inches wide. This fungus is the Panaeolus speciosus, or Orton Schaf-Dungerling, which is beige to dull brown and grayish and darker in color around the edges of the cap. The stem is whitish-beige or grayish-pink with a dusted-white base.
Find the Panaeolus subbalteatus, or Garten-Dungerling, growing on horse manure in early summer to autumn. This fungus also has a stem much longer than the cap's diameter. The convex to flat-shaped cap is ¾ inch to 2½ inches wide that is dark reddish-brown. The stem is lighter in color, a pale brown.