Uses of Hypericum
Some species are used as ornamental plants and have large, showy flowers. Numerous hybrids and cultivars have been developed for use in horticulture, such as Hypericum × moserianum (H. calycinum × H. patulum) and Hypericum calycinum cv. 'Hidcote'.
St. John's-worts can occur as nuisance weeds in farmland and gardens. On pastures, some can be more than a nuisance, causing debilitating photosensitivity and sometimes abortion in livestock. The beetles Chrysolina quadrigemina, Chrysolina hyperici and the St. John's-wort Root Borer (Agrilus hyperici) like to feed on Common St. John's-wort (H. perforatum) and have been used for biocontrol where the plant has become an invasive weed.
Hypericum species are the only known food plants of the caterpillar of the Treble-bar, a species of moth. Other Lepidoptera species whose larvae sometimes feed on Hypericum include Common Emerald, The Engrailed (recorded on Imperforate St. John's-wort, H. maculatum), Grey Pug and Setaceous Hebrew Character.
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