Mycochytridiales

an order of lower fungi of the subclass Archimycetes (formerly considered to be a class) of the class Phycomycetes. The vegetative body of Mycochytridiales consists of a single cell with a nucleus in the center or of several, for the most part, rounded cells. Such cells are covered with a sheath from the beginning of their development and have more or less developed slender rhizoids, which are usually entirely submerged in a nutritive substrate. Mycochytridiales live either on the surface of or, to some degree, submerged in the tissue of a plant or animal host. Asexual reproduction is by means of uniflagellate zoospores, which originate in the zoosporangium as a result of repeated division of its nucleus; the zoosporangia develop from the central cell. In some species, a sexual process, in the form of the merging of two mature individuals, has been observed. Sometimes resting spores are formed, which later sprout into ordinary zoosporangia or develop immediately into zoospores.

The majority of Mycochytridiales are saprophytes and para-sites of aquatic plants. Some species are parasites of higher terrestrial plants, such as Urophlyctis alfalfae, which parasitizes alfalfa; U. leproides, which parasitizes sugar beet; Physoderma zeae-maydis, which parasitizes corn; and P. graminis, which parasitizes wheat.