Psathyrella hymenocephala is a species of mushroom in the family Psathyrellaceae, widely known in Haitian cuisine as djon djon. It is native to the Caribbean region, particularly Haiti, where it grows in forested environments, often in association with decaying organic matter. The genus name Psathyrella derives from Greek psathuros, meaning “friable” or “crumbly,” referring to the delicate, brittle texture of mushrooms in this group, while the species epithet hymenocephala combines hymen (“membrane”) and kephalē (“head”), likely describing structural features of the cap and spore-bearing surface. The vernacular name djon-djon comes from Haitian Creole and is used specifically for this culinary mushroom and for Psathyrella coprinoceps which is also edible and appears identical to P. hymenocephala without a microscope.

The mushroom is small and dark-colored, with thin flesh and a fragile structure typical of Psathyrella species. It grows seasonally and is traditionally harvested in the wild rather than widely cultivated. After harvesting, it is usually dried, which concentrates its flavor and allows for storage and transport. When rehydrated or cooked, djon-djon releases a dark pigment that colors dishes a characteristic gray to black hue.

As a food source, Psathyrella hymenocephala is highly valued for its distinctive earthy, smoky, and umami-rich flavor. It is a defining ingredient in Haitian cuisine, most famously in diri ak djon-djon, a rice dish in which the mushrooms are boiled to extract both flavor and color, and the resulting liquid is used to cook rice along with aromatics and sometimes seafood or meat. The mushrooms themselves may also be chopped and incorporated into the dish. Beyond rice, djon-djon is used in sauces, stews, and soups, where it imparts both depth of flavor and a dark coloration.

Chemically, like many mushrooms, Psathyrella hymenocephala contains polysaccharides such as β-glucans, which have been studied for immunomodulatory effects, as well as amino acids that contribute to umami taste. The dark pigment released during cooking is not fully characterized but likely consists of melanin-like compounds and other phenolic substances formed during growth and drying. The mushroom also provides dietary fiber, small amounts of protein, and micronutrients typical of edible fungi.