the name for any of a group of lower fungi of microscopic size and primitive structure, mostly unicellular and mononuclear. The mycelium in chytrids is either totally lacking or weakly branched and atypically structured. The fungi are mainly aquatic organisms that live as saprophytes or parasites on algae, microscopic animals, or other fungi; they occasionally live on terrestrial plants.
The group includes more than 90 genera, embracing approximately 500 species, which are distributed throughout the world. Some species cause plant diseases, for example, blackleg of cabbage (Olpidium brassicae) and powdery scab of potato wart (Synchytrium endobioticum). In Soviet writings on botany, chytrids are sometimes called Archimycetes.