Bolbitius titubans, also known as Bolbitius vitellinus, and commonly known as the sunny side up[1] is a widespread species of mushroom found in America and Europe.

It grows chiefly on dung or heavily fertilized soil, and sometimes on grass.

[2] The mushroom cap is between 1.5–7 cm,[3] and grows from egg-shaped when young to broadly convex, finally ending up nearly flat.

[5] The gills are free from the stem or narrowly attached to it, are fragile and soft, and fade from whitish or pale yellowish to rusty cinnamon with age.

[4] The stem is 3–12 cm tall and 2–6 mm wide,[3] is whitish-yellow with a fine mealy powdering, and is very delicate.