Abstract
Four species of Hypericum growing in Italy were characterized morphologically and chemically: Hypericum perforatum L., H. maculatum Crantz., H. calycinum L. and H. pulchrum L. The composition of secondary metabolites (phloroglucinols, naphthodianthrones, flavonoids) in the aerial parts of plants collected in different habitats was analysed. The four species show different compositions of phloroglucinols and naphthodianthrones, but there was no qualitative difference in flavonoid content of the species analysed. Study of main-constituent variation during the ontogenetic cycle showed that hypericin decreases and hyperforin increases during the reproductive phase. In St. John's Wort, hypericin and hyperforin are thought to be localised in black nodules. Our investigation shows no clear correlation between either the presence or absence of nodules and hypericin or hyperforin content.