A number of often conflicting, morphology-based classifications have been suggested for the Xylariales. However, no attempt has previously been made to test these classifications using molecular data. Phylogenetic relationships of 6 accepted families of the Xylariales (Amphisphaeriaceae, Clypeosphaeriaceae, Diatrypaceae, Graphostromataceae, Hyponectriaceae and Xylariaceae) plus members of the Apiosporaceae, were investigated using individual and combined analyses of 28S and 18S rDNA gene fragments. Analyses were conducted using maximum and weighted parsimony, and likelihood criteria. The Xylariales was found to be a monophyletic order containing the above 7 families. However, the 28S and 18S rDNA data proved to be inadequate in determining the familial relationships within the order. This finding is contrary to most other studies in ascomycete systematics using these particular genes.

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