It produces small, dark, pustular, gelatinous basidiocarps (fruit bodies) and is parasitic on pyrenomycetous fungi (Diaporthe and Cucurbitaria species) on dead branches of trees and shrubs.

Tremella exigua was first published in 1847 by French mycologist John Baptiste Desmazières based on a collection from France on a dead branch of ash (Fraxinus excelsior).

[1] Swedish mycologist Elias Magnus Fries had earlier described Agyrium atrovirens, a species interpreted as synonymous with T. exigua, on the same host tree from Sweden.

[6] Species of Nostoc are greenish black and gelatinous, but are cyanobacteria (not fungi) and form growths that are typically more extensive and often terrestrial.

Though originally described from ash, the species is more commonly found on dead branches of gorse (Ulex europaeus), broom (Cytisus scoparius), and barberry (Berberis vulgaris).