citronella, common name for a grass, Cymbopogon nardus, the source of oil of citronella, used in perfumes and soaps and as an insect repellent. The plant, with bluish green, lemon-scented leaves, is cultivated in Java and Sri Lanka. Citronella is classified in the division Magnoliophyta, class Liliopsida, order Cyperales, family Gramineae.