- Phytophthora is a genus of parasitic oomycetes that infect plants. It contains 48 cosmopolitan species that are facultative parasites or saprophytes. - One well-known species is P. infestans, which causes late blight in potatoes. It appears as small black or purple lesions on leaves and can rot tubers if conditions are moist. - Phytophthora has coenocytic, aseptate mycelium that branches monopodially. It reproduces vegetatively through chlamydospores and asexually via sporangia borne on sporangiophores. Zoospores released from sporangia are biflagellate. Sex