​ST JOHN'S WORT, in botany, the general name for species of Hypericum, especially H. perforalum, small shrubby plants with slender stems, sessile opposite leaves which are often dotted with pellucid glands, and showy yellow flowers. H. Androsaenium is Tutsan (Fr. tout saine), so called from its healing properties. H. calycinum (Rose of Sharon), a creeping plant with large almost solitary flowers 3 to 4 in. across, is a south-east European plant which has become naturalized in Britain in various places in hedges and thickets.