18S rDNA for species of Leptolegnia and other Peronosporomycetes:: justification for the subclass taxa Saprolegniomycetidae and Peronosporomycetidae and division of the Saprolegniaceae sensu lato into the Leptolegniaceae and Saprolegniaceae

The 18S rDNA data base for mainstream Peronosporomycetes has been substantially increased. The sub-class divide between the Peronosporomycetidae and the Saprolegniomycetidae is supported. The deep clade separation of the Leptomitales within the Peronosporomycetidae is reinforced and support is provided for divergences within the Phytophthora and Pythium lines. A new family for the Leptolegnia lineage is proposed from the Saprolegniaceae sensu lato.