[3] They typically develop within plant cells, causing the infected tissue to grow into a gall or scab.

Important diseases caused by phytomyxeans include club root in cabbage and its relatives, and powdery scab in potatoes.

Both resting spores and motile zoospores, which generally have two smooth flagella, are produced at different stages.

Plasmodiophorids were traditionally considered slime moulds, because of the plasmodial stage and are often wrongly classified as fungi, and given names such as the Plasmodiophoromycota.

However, genetic and ultrastructural studies indicate they belong to a diverse group of protists called the Cercozoa, are closely related to them.