phylum of plant parasites in the kingdom Chromista commonly referred to as endoparasitic slime molds. Some scientists assign Plasmodiophoromycota to the kingdom Protista. The most important genera are Plasmodiophora and Spongospora.

All members are obligate parasites of algae, fungi, or plants, causing cell enlargement, especially of the roots. They are distinguished by the production of motile cells (zoospores) with two unequal anterior whiplike threads (flagella).

Plasmodiophora brassicae causes clubroot of cabbage and related plants. Spongospora subterranea causes powdery scab of potato.