Peronosporales form an internal parasitic mycelium within a host plant. In different structures conidia are formed. They germinate while forming motile spores that than reinfect a host plant. Within the host plant by sexual means thick-walled oospores are formed that enable hibernation. The oospores germinate and form similar motile spores as just mentioned. The ornamentation of the oospore wall often is an important diagnostic character.

mod 21.vii.2017