Definition of perforate St John's-wort in US English:

perforate St John's-wort

noun

  • A perennial herbaceous hypericum having leaves dotted with translucent oil glands, Hypericum perforatum, native to Europe and Asia and introduced elsewhere, and widely used in herbal medicine; (in early use also, usually with distinguishing word) †any of several other hypericums having such leaves, especially H. humifusum (obsolete).

Origin

Mid 18th century.