Oomycota

The Oomycota is the phylum containg fungal-like organisms commonly referred to as water molds or oomycetes. Although many of these microorganisms do occur in water, some are devastating plant pathogens and still others are soil borne saprobes. 

Although oomycetes and true fungi are unrelated, they share some physical traits. Like fungi, oomycetes generally have a filamentous body composed of threadlike hyphae. Oomycetes also have a nutritional mode like fungi. Both groups are absorptive heterotrophs, producing enzymes that are secreted into the environment and break down complex organic compounds into smaller molecules. Despite these similarities, oomycetes have many biochemical, ultra­structural, life cycle, and phylogenetic differences that separate them from fungi. The cell wall of oomycetes contains cellulose, in contrast to chitin in the cell wall of true fungi. 

The characteristic sexual structure of oomycetes is the oogonium, which contains one or more oospores that result from fertilization. Oospores are thick-walled dormant structures that are not dispersed and remain where they formed. In the more advanced members of the phylum, only a single oospore develops in the oogonium

Asexual reproduction in the Oomycota is varied. Many members of this phylum form zoospores, motile asexual spores that are produced in sporangia and are dependent on water for dispersal. By contrast, some oomycetes are known to produce sporangia that are dispersed by wind. These include some well-known plant pathogens that have had a major impact on society, such as the organisms that cause late blight of potato and downy mildews.