Charles Henri Marie Flahault (3 October 1852 – 3 February 1935) was a French botanist, among the early pioneers of phytogeography, phytosociology, and forest ecology. The word relevé for a plant community sample is his invention.
Flahault was born in Bailleul, Nord, and received his Baccalauréat de Lettres at Douai in 1872, after which he became a gardener at the Jardin des Plantes de Paris. He was noticed by Joseph Decaisne (1807–1882), who gave him private lessons, after which he entered the Sorbonne in 1874 to study in the laboratory of Philippe Van Tieghem (1839–1914),
obtaining his doctoral degree in biology in 1878. He continued his studies at Uppsala University in 1879 together with Gaston Bonnier.
In 1881 joined the University of Montpellier where in 1883 he became professor of botany, and in 1890 he founded the Institut de Botanique. The Swiss botanist Josias Braun-Blanquet was one of his students
In 1888 Flahault was elected member of the Royal Physiographic Society in Lund, 1905 to the Royal Society of Sciences in Uppsala (1905), and in 1907 he was awarded an honorary doctor at Uppsala University.
He resided in Montpellier until his death, and is buried in that city's Cimetière Saint Lazare.
Several plant species have been named to his honour.
Recherches sur l’accroissement terminal de la racine chez les phanérogames (thèse de doctorat), G. Masson, Paris, 1878 (198 pp., 8 pl.)
Observations sur les modifications des végétaux suivant les conditions physiques du milieu, An. Sc. Nat. Bot. 6, VII, p. 93-125, 1878 (avec Gaston Bonnier).
Nouvelles observations sur les modifications des végétaux suivant les conditions physiques du milieu, An. Sc. Nat. Bot. 6, IX, p. 159-207, (1878).
Phénomènes périodiques de la végétation d’après les travaux météorologiques scandinaves, 1878
Nouvelles observations sur les modifications des végétaux suivant les conditions physiques du milieu, B.S.B.F., XXXVI, p. 346-350, (1879).