On Geastrum argentinum, a forgotten species

•An epitype of Geastrum argentinum is proposed.•Taxonomy of Geastrum argentinum is discussed.•Geastrum argentinum is a good species.

Geastrum argentinum, a long forgotten species described by Spegazzini and previously regarded by Soto and Wright (2000) as a synonym of G. fimbriatum, has been found in several locations in Argentina. A careful analysis revealed relevant differences between those taxa, proving the validity of Spegazzini's species. Here we re-describe Spegazzini's species from the damaged type material and from new fresh collections, proposing one of them as an epitype.