Oomycota (Water Molds and Downy Mildews)

"The Oomycota have been excluded from the kingdom Fungi primarily because their cell walls are made of cellulose rather than chitin. They also have swimming zoospores with two flagella (one whiplash and one tinsel), large nuclei, large egglike oospores, and various other nonfungal-like features. They are closely related to the brown algae (kelps) and diatoms, but of course lack chloroplasts. These organisms are now placed as heterokonts in the kingdom Stramenopila (or the catch-all dumping-ground kingdom Protista according to some authors). Ecologically many of its members act like fungi, especially the plant pathogens. Phytophthora infestans causes a disease called late blight of potato, which was the cause of the Irish potato famine in the 1840s, in which more than a million Irish people perished and another million emigrated. The downy mildews Peronospora parasitica and Plasmopara viticola cause diseases of members of the cabbage family and of grapes, respectively. Pythium species cause damping-off disease of seedlings in agricultural practice. However, many other species are innocuous saprophytes that decompose debris in water. A few of these so-called water molds (some species of Saprolegnia and Achlya) are opportunistic fish parasites, especially in aquariums and fish hatcheries. They are a particular problem in trout and salmon hatcheries." (p. 630)

Source: Volk, Thomas J. (2013). Fungi, pp. 624-640. In: Encyclopedia of Biodiversity (Second Edition). Elsevier. [Abstract]

Class: Oomycetes

Order: Lagenidiales

Family: Lagenidiaceae

—No subordinate taxa

Family: Olpidiosidaceae

—No subordinate taxa

Family: Sirolpidiaceae

—No subordinate taxa

Order: Leptomitales

Family: Leptomitaceae

—No subordinate taxa

Order: Peronosporales

Family: Albuginaceae

—No subordinate taxa

Family: Peronosporaceae

Family: Pythiaceae

—No subordinate taxa

Order: Rhipidiales

Family: Rhipidaceae

—No subordinate taxa

Order: Saprolegniales

Family: Ectrogellaceae

—No subordinate taxa

Family: Haliphthoraceae

—No subordinate taxa

Family: Leptolegniellaceae

—No subordinate taxa

Family: Saprolegniaceae

—No subordinate taxa

Class: Peronosporea

Order: Leptomitales

Family: Leptolegniellaceae

Order: Olpidiopsidales

Family: Olpidiopsidaceae