Current status of the plasmodiophorids.

Plasmodiophorids are a monophyletic group with uncertain systematic affinities. Features of the group include cruciform nuclear division; obligate, intracellular parasitism; biflagellated, heterocont zoospores; and environmentally resistant resting spores. Economically significant members of the group include Plasmodiophora brassicae, the causative agent of clubroot of cabbage; Spongospora subterranea, the causative agent of powdery scab of potato; and two members of the genus Polymyxa, vectors for several plant pathogenic viruses.