pythiaceae pythiaceae pythiaceae is a family of water moulds. the family includes serious plant and animal pathogens in the genus pythium. the family was circumscribed by german mycologist joseph schröter in 1893. pythiaceae water mould - phytophthora forms: a: sporangia. b: zoospore. c: chlamydospore. d: oospore scientific classification kingdom: chromista phylum: oomycota order: peronosporales family: pythiaceaej. schröt., 1893 type genus pythiumpringsh., 1858 genera cystosiphon diasporangium globisporangium lagenidium myzocytium pythium trachysphaera lifecycle live on land (terrestrial), and in water (aquatic), and a combination of the two, (amphibious) live as deadly parasites, causing some serious plant and animal diseases when terrestrial. the diploid (2n) life stage predominates, with a short haplophase initiated during sexual reproduction as well as asexual reproduction (homothallism predominates in the family) to fuse gametes. reproduction the sporangia may germinate via a germ tube or by release of motile zoospores, depending on the species and the environmental conditions. economic importance some pythium species cause "damping off" diseases in young plants (seedlings).