Marie Maxime Cornu (July 16, 1843 – April 3, 1901) was a French botanist and mycologist. He was a younger brother to physicist Alfred Cornu (1841-1902).
Cornu was a lecturer at the Museum National d'Histoire Naturelle in Paris, and from 1884 to 1901 was chair of horticulture at the museum. He is remembered for his research of cryptogams and agents of plant diseases, particularly phylloxera vastatrix, a pest that caused extensive damage to French vineyards and wine-production.