Ribosomal RNA sequence phylogeny is not congruent with ascospore morphology among species in Ceratocystis sensu stricto

The genus Ceratocystis sensu stricto includes important fungal pathogens ofwoody and herbaceous plants. This genus is distinguished from species inCeratocystis sensu lato by the presence of Chalara anamorphs. Ascosporeshape has been used extensively in delineating Ceratocystis taxa, whichshow a large variety of ascospore shapes. Sequence analysis of one regionof he 18S ribosomal RNA subunit and two regions of the 28S ribosomal RNAsubunit showed that there was a majority of multiple substitutions atnucleotide sites and that there was a low transition/transversion ratio, T= 0.72. Both of these results suggest that these are well established, oldspecies. Ascospore morphology, for the most part, was not congruent withthe molecular phylogeny, and the use of morphological characters may bemisleading in the taxonomy of these species.