Morphological variability and implication for definition of taxa in the Descolea-Setchelliogaster-Descomyces complex

Morphological continuums, which transgress traditional taxonomic boundaries , are expressed by many taxa within the Descolea-Setchelliogaster-Descomyce s complex. We examine the contention that key macroscopic and microscopic c haracters traditionally used to distinguish some taxa of the complex are qu antitatively variable components of the same taxon. We focus on Setchelliog aster and synonymize S. rheophyllus under S. tenuipes. Synonymy is necessar y because form of basidioma/hymenium and occurrence of cystidia is highly v ariable within and between collections variously ascribed to these species. There is a direct relationship between the type of hymenial development an d the abundance of cystidia. Other examples of high morphological variabili ty within taxa of the complex are shown with Descolea maculata, D. gunnii a nd S. australiensis. Implications of variability in taxa include: (a) Gener ic names defined by basidiomal form are categories useful in a broad practi cal sense but may not be biologically distinct as their boundaries are tran sgressed by some taxa, e.g. D. maculata has forms typical of Descolea and S etchelliogaster. (b) Variations in basidiomal form expressed by taxa may be strong or weak. Broader species concepts than currently recognised are nec essary for some species.