Seasonal variation in phenolics in leaves of Celtis australis (Cannabaceae)

► 21 Phenolics were quantified in leaves of Celtis australis by RP-HPLC. ► The content of all phenolics was highest in young leaves. ► Phenolic contents decreased during the first six weeks of the growing season. ► Afterwards levels remained stable until the end of the growing season. ► Implications for the optimal harvesting time of medicinal plants are discussed.