Phylogenetic analyses of partial sequences (1002 basepairs) from the nuclear encoded small subunit ribosomal RNA (18S rRNA) were performed to determine the phylogenetic relationships of the ascostromatic fungi, Botryosphaeria, Guignardia, Leptosphaerulina, Didymella, Venturia, Sporormia, and Sporormiella. Our studies confirm the concept that the subclass Loculoascomycetidae is paraphyletic if Chaetothyriales is included, as this order and the plectomycetes constitute a monophyletic clade that is highly supported in our and some previous phylogenetic analyses. In general, taxa that lack pseudoparaphyses (Dothideales) or have reduced hamathecial tissue, such as Botryosphaeria and Guignardia (sensu Sivanesan), are a sister group to the Pleosporales, the most derived group, whose members have pseudoparaphyses. The two species of Leptosphaerulina, which also lack pseudoparaphyses, clustered within the Pleosporales, rather than within the Dothideales, with high confidence from bootstrap values. Didymella nested within the Pleosporales with a high degree of confidence, and is the sister group to Leptosphaerulina. The taxonomic placement of Venturia and Sporormiella corresponds to the Pleosporales.
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