Some of the homobasidiomycete group of fungi, which includes most of the mushrooms with which we are familiar, have earned exotic names such as bird's nest and puffball because of the appearance of their fruiting bodies (the part of the fungus that produces the spores).

Traditional classification divides this group into the gilled fungi (which have fruiting bodies with a cap and a gilled underpart containing the spores) and the puffballs and relatives (in which the spores are enclosed within variously shaped fruiting bodies). The gilled species expel their spores by an elaborate ballistic mechanism (ballistospory) whereas the puffballs for instance slowly crumble, gently releasing their cargo. Although fruiting bodies are diverse in appearance their anatomy is very simple. This, coupled with the dearth of fossil evidence, has made it difficult to unravel the fungal family tree.

Writing in The Proceedings of the National Academy of Sciences (94, 12002-12006; 1997), David Hibbett and colleagues have tackled the complexities of fungal evolution by molecular analyses of 81 species. They compared the nucleotide sequences of various genes and drew up a family tree based on the similarity of sequences between different species.

It turns out that the same gill-and-cap style of fruiting body evolved at least six times. Furthermore, some of the puffballs and their relatives arose from their gilled cousins whereas others, such as the bird's nest fungus (Crucibulum laeve; shown here), developed independently. It seems that the group including the puffballs never evolved into gilled mushrooms — the authors surmise that ballistospory can develop into other forms of dispersal, but the reverse has not occurred.