Allomyces macrogynus is a saprobic homothallic fungi from the order Blastocladiales. It exhibits two very similar looking dichotomously branching, coenocytic thalli while immature. However, once the thalli have reached maturity the orange male gametangia growing epigynously on the clear female gametangia make the haploid gametothallus differentiable from the diploid sporothallus that produces terminal sporangia. The gametangia produce small haploid posterior, uniflaggellate gametes. The female gamete is much less motile than the male gamete and diffuses a hormone called Sirenin to attract the male gamete. Upon gamete fusion a large posterior biflaggelate zygote is produced that encysts to form the sporothallus. On a single sporothallus both pigmented resistant sporangia and clear zoosporangia can be produced. The thick-walled, melanin pigmented, resistant sporangia are the site of meiosis and release haploid zoospores into an exit papilla prior to release into the water. The haploid zoospores later encyst to form the gametothallus.
