Bolbitius titubans, also known as Bolbitius vitellinus, and commonly known as the sunny side up, is a widespread species of mushroom found in North America. It grows on grass and dung.

Description

The mushroom cap is 1.5–7 centimetres (1⁄2–3 in) across, and grows from egg-shaped when young to broadly convex, finally ending up nearly flat. The cap's color starts yellow or bright yellow, and fades to whitish or greyish with age. The stem is 3–12 cm (1–4+1⁄2 in) tall and 2–6 millimetres (1⁄8–1⁄4 in) wide, whitish-yellow with a fine mealy powdering, and very delicate.

The fragile and soft gills are free from the stem or narrowly attached and fade from whitish or pale yellowish to rusty cinnamon with age. They produce a rusty-brown spore print. The spores are brown, elliptical, and smooth.

Similar species

Similar species include Bolbitius aleuriatus, B. coprophilus, B. lacteus, and Conocybe apala.

Habitat and distribution

The species grows on grass, woodchips, compost, and dung. It is ubiquitous in North America and Europe.

Edibility

The mushroom's edibility is unknown. While nonpoisonous, it is too small to be worthwhile.