A puffball is a member of any of a number of groups of fungus in the division Basidiomycota. The puffballs were previously treated as a taxonomic group called the Gasteromycetes or Gasteromycetidae, but they are now known to be a polyphyletic assemblage. Their distinguishing feature is that they have gasterothecia (gasteroid basidiocarps) in which the spores are produced internally; that is, the basidiocarp remains closed, or opens only after the spores have been released from the basidia.