Phytophthora cryptogea is a species of water mould in the family Pythiaceae.

[1] Like its relative Phytophtora cambivora, it can cause ink disease of chestnuts (Castanea sativa).

Progression of lesions leads to girdling, root system rot and plant collapse.

It reproduces asexually through sporangiophores and accompanying non-papillate sporangia in liquid media as well as by uneven, irregular hyphal growth.

[2] Sexual reproduction is heterothallic, typically requiring an opposite mating type but sometimes occurring in aged single cultures.