Age-related variation of polyphenol content and expression of phenylpropanoid biosynthetic genes in Agastache rugosa

•Phytochemical and gene expression profiles of Agastache rugosa depend on vegetation age and the age of mother plants.•Major phenolics differed significantly between plants of different age and different age of a mother plant.•ArRAS (encoding rosmarinic acid synthase) is the rate-limiting step for RA biosynthesis.•An existence of a transgenerational phenomenon is suggested.•Plant age and the age of progenitors should be considered in perennial herbs cultivation.