Panaeolina foenisecii

Panaeolina foenisecii is a very common and widely distributed little brown mushroom often found on lawns and never contains the hallucinogen psilocybin, despite several erroneous reports to the contrary. In 1963 Tyler and Smith found that this mushroom contains serotonin, 5-htp, and 5-hydroxyindoleacetic acid.

It is sometimes mistaken for the hallucinogenic Panaeolus subbalteatus, which has jet black spores.

Description
This is a common little brown mushroom that grows in lawns and has very dark brown spores. The cap is up to 3 cm across, chestnut brown to tan, hygrophanous, and campanulate to convex. The stem is 6 cm by 25 mm, pruinose and twisted at the top.