Geoglossum is a genus of fungi in the family Geoglossaceae. They are commonly called earth tongues. The type species is Geoglossum glabrum. Geoglossum species are distinguished from the related genus Trichoglossum by the lack of setae on the spore bearing surface. Geoglossum species are characterized by dark, club-shaped, terrestrial ascocarps with a fertile hymenium continuing downward from the apex of the ascocarp along the stipe, eventually intergrading with a sterile stipe. The ascospores of Geoglossum range from translucent to dark brown, and are fusiform, and multiseptate. Identification of species is based on the gross morphology of the ascocarp, color and septation of the ascospores, and shape and ornamentation of the paraphyses.

Geoglossaceae is a family of fungi in the order Geoglossales, class Geoglossomycetes. These fungi are broadly known as earth tongues. The ascocarps of most species in the family Geoglossaceae are terrestrial and are generally small, dark in color, and club-shaped with a height of 2–8 cm. The ascospores are typically light-brown to dark-brown and are often multiseptate. Other species of fungi have been known to parasitize ascocarps. The use of a compound microscope is needed for accurate identification.