Scarlet Bonnet

The cap initially has a sharply conic shape, but expands to a narrow bell-shape or a broad cone in maturity, typically reaching 0.5 to 1.2 cm (1⁄4 to 1⁄2 in) in diameter. It is scarlet red when young, becoming orange to yellowish. The cap margin, which is initially pressed against the stem, is opaque or nearly so at first. The mushroom is hygrophanous, and fades to an orange buff when dry. The flesh is thin, the same color as the cap, fragile, and without any distinctive taste or odor. The gills are ascending-adnate (attaching at much less than a right angle, appearing to curve upward toward stem) or attached by a tooth, subdistant to close, with 14–16 gills reaching the stem. Additionally, there are two or three tiers of lamellulae—short gills that do not extend fully from the cap edge to the stem. The gills are narrow, and yellowish or with a reddish tinge at first; the margins are paler and the same color as the faces. The stem is 2–4 cm (3⁄4–1+5⁄8 in) long and 1–2 mm (1⁄32–3⁄32 in) thick, and roughly equal in width throughout. It is tubular, fragile, initially pruinose (covered with a fine powder), polished and smooth with age, pale yellow, becoming whitish, with the base often dirty yellow or brownish.

Microscopic characteristics. The spores are narrowly ellipsoid, inamyloid, and measure 6–7 by 3–3.5 μm. …

The fruit bodies of A. adonis grow solitarily or in groups in conifer forests and heaths, and appear in the spring and autumn. The fruit bodies grow in groups or scattered on needle beds under spruce and hemlock in wet coastal conifer forests, or in the higher mountains, where it is not uncommon in the spring and autumn months. The fungus is found in Europe and in western North America, where Mycena specialist Alexander H. Smith found the species in Washington, Oregon, and California. In 2007, it was reported from the valley of the Ussuri River in the northeast of China.

In one instance, fruit bodies were found growing on the deciduous trees Spanish Maple (Acer granatense) and willow (Salix alba) near Amsterdam. It was hypothesized that the bark of these trees had become more acidic in recent years because of increasing atmospheric pollution (specifically, increases in the levels of sulfuric and nitric acid from industrial smoke), providing a more suitable substrate for the fungus.

The species epithet refers to the handsome youth Adonis in Greek mythology. Samuel Frederick Gray called it the "Adonis high-stool" in his 1821 Natural Arrangement of British Plants, while Mordecai Cubitt Cooke named it the "delicate Mycena".