The Oomycetes (/ˌoʊ.əˈmaɪsiːts/),[3] or Oomycota, form a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms within the Stramenopiles.

One oomycete, the mycoparasite Pythium oligandrum, is used for biocontrol, attacking plant pathogenic fungi.

However, molecular and phylogenetic studies revealed significant differences between fungi and oomycetes which means the latter are now grouped with the stramenopiles (which include some types of algae).

The oomycetes rarely have septa (see hypha), and if they do, they are scarce,[7] appearing at the bases of sporangia, and sometimes in older parts of the filaments.

[9][10] Haptoglossales Eurychasmales Haliphthorales Olpidiopsidales Atkinsiellales Saprolegniales Leptomitales Rhipidiales Albuginales Peronosporales This group was originally classified among the fungi (the name "oomycota" means "egg fungus") and later treated as protists, based on general morphology and lifestyle.

The main dispersive spores are asexual, self-motile spores called zoospores, which are capable of chemotaxis (movement toward or away from a chemical signal, such as those released by potential food sources) in surface water (including precipitation on plant surfaces).

They also produce sexual spores, called oospores, that are translucent, double-walled, spherical structures used to survive adverse environmental conditions.