Phytophthora cryptogea is a species of water mould in the family Pythiaceae. It is a plant pathogen that infects several species of cultivated plants, including over 40 species of cultivated flowers. This species is reported to be pathogenic on grandiflora petunia (Petunia × atkinsiana). It causes root rot, shoot rot and shanking in tulips. It also infects blue daze (Evolvulus glomeratus), dusty miller (Senecio cineraria), Barberton daisy (Gerbera jamesonii), and garden verbena (Verbena × hybrida). Like its relative Phytophtora cambivora, it can cause ink disease of chestnuts (Castanea sativa).