Calostoma is a genus of 29 species of gasteroid fungi in the suborder Sclerodermatineae. Like other gasteroid fungi, Calostoma do not have the spore discharge mechanism associated with typical gilled fungi (ballistospory), and instead have enclosed spore-bearing structures. Resembling round puffballs with raised, brightly colored spore openings (ostioles), elevated on a thick, gelatinous stalks, species have been collected in regions of deciduous, temperate, tropical or subtropical forests. Their distribution includes eastern North America, Central America, Asia, and Australasia. The common name given to some species, "prettymouth", alludes to the brightly colored raised openings (ostioles) that may somewhat resemble lips. Other common names include "hotlips" and "puffball in aspic".

The unusual fruit body structure has historically led mycologists to suggest various classification schemes based on presumed relationships to other puffball or "stomach mushrooms". Phylogenetic analyses performed in the 2000s show the genus to be evolutionarily related to the Bolete mushrooms. Calostoma species are ectomycorrhizal, forming symbiotic associations with trees from various families. The type species, Calostoma cinnabarinum, is ectomycorrhizal with oak.

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