Peronosporaceae are a group of endophytic parasites - about ioo species - of great importance as comprising the agents of "damping off" disease (Pythium), vine-mildew (Plasmopara), potato disease (Phytophthora), onion-mildew (Peronospora).
The Peronosporaceae reproduce themselves sexually by means of antheridia and oogonia as described in Pythium.
The sexual reproduction shows all transitions between forms which are normally sexual, like the Peronosporaceae, to forms in which no antheridium is developed and the oospheres develop parthenogenetically.
The oogonia, unlike the Peronosporaceae, contain more than one oosphere.