French botanist (1857–1936).
Julien Noël Costantin (16 August 1857 – 17 November 1936) was a French botanist and mycologist who was a native of Paris. He studied at École Normale Supérieure on the Rue d'Ulm. In 1881 he received his license in natural history and two years later earned his doctorate. In 1883 he was appointed adjunct professor at Bordeaux, and through influence from Philippe Van Tieghem (1839-1914), became an assistant naturalist at the Muséum national d'histoire naturelle shortly afterwards. In 1887 Costantin became a lecturer of botany at Ecole Normale Superieure. In 1901 he succeeded Marie Maxime Cornu.