Spatio-temporal variation of the diterpene steviol in Stevia rebaudiana grown under different photoperiods

► Steviol is the aglycone of the sweet steviol glycosides in Stevia rebaudiana. ► Free steviol level in leaves is at least 1000-fold smaller than that of its glycosides. ► Steviol content is strongly influenced by photoperiod and genotype. ► A general decrease was seen after flower opening. ► Under short-days, a linear correlation exists between steviol and its glycosides.