Gerronema is a genus of small- to medium-sized lignicolous agarics with white, nonamyloid, spores and decurrent gills.

[4] Typically the cap of the fruit bodies have a shallow to deep central depression, giving the umbrella-like to funnel-shaped caps the appearance of a belly button, or a belly with a navel.

Gerronema belongs to the informal “hydropoid” clade, together with Hydropus, Megacollybia and Clitocybula.

[7] The species have a primarily tropical distribution, but also occur in Europe and eastern North America where they fruit during hot muggy, summer weather.

As of June 2015[update], Index Fungorum lists 55 species in Gerronema:[8] and a new combination was published in 2019.