EVOLUTION OF GILLED MUSHROOMS AND PUFFBALLS INFERRED FROM RIBOSOMAL DNA-SEQUENCES

Homobasidiomycete fungi display many complex fruiting body morphologie s, Including mushrooms and puffballs, but their anatomical simplicity has confounded efforts to understand the evolution of these forms, Wt performed a comprehensive phylogenetic analysis of homobasidiomycetes, using sequences from nuclear and mitochondrial ribosomal DNA, with an emphasis on understanding evolutionary relationships of gilled mushro oms and puffballs. Parsimony-based optimization of character states on our phylogenetic trees suggested that strikingly similar gilled mushr ooms evolved at least six times, from morphologically diverse precurso rs, Approximately 87% of gilled mushrooms are in a single lineage, whi ch we call the ''euagarics.'' Recently discovered 90 million-year-old fossil mushrooms are probably euagarics, suggesting that (i) the origi n of this clade must have occurred no later than the mid-Cretaceous an d (ii) the gilled mushroom morphology has been maintained in certain l ineages for tens of millions of Sears, Puffballs and other forms with enclosed spore-bearing structures (Gasteromycetes) evolved at least fo ur times, Derivation of Gasteromycetes from Forms with exposed spore-b earing structures (Hymenomycetes) is correlated with repeated loss of forcible spore discharge (ballistospory). Diverse fruiting body forms and spore dispersal mechanisms have evolved among Gasteromycetes, Neve rtheless, it appears that Hymenomycetes have never been secondarily de rived from Gasteromycetes, which suggests that the loss of ballistospo ry has constrained evolution in these lineages.