Common St. Johnswort

Prepared by Jennifer L. D’Appollonio, Assistant Scientist, University of Maine, Orono, ME 04469. Updated April 2019.

Scientific name: Hypericum perforatum L.

Common name(s): common St. Johnswort, St. Johnswort

Link(s): USDA PLANTS Profile, Go Botany

Images: (to see enlargements [PC]: click on image, then right click and choose “view image”)


– perennial

– generally flowers July, August in ME

Stems reddish and branching, 1′-2.5′ tall, woody at base.  Leaves oblong, entire, sessile, up to 1.5″ long with numerous, conspicuous translucent dots.  Numerous, five-parted yellow 3/4″-1″ wide flowers clustered at branch ends.

-spreads through rhizomes, stems, and seeds


-fields, shores of rivers, man-made disturbed areas


-Hand pulling

  • only on new small plants

-biological control, species that feed off their leaves

  • Chrysolina quadrigemina
  • hrysolina hyperici
  • Aplocera plagiata
  • Agrilus hyperici

Over exposure can lead to health problems

  • skin lesions
  • necrosis

– may be confused with H. punctatum, which has black dots/streaks over the whole petal, whereas H. perforatum has black near the margins; see left sidebar of Go Botany webpage


Heinrich, B. 1976. Flowering phenologies: Bog, woodland, and disturbed habitats. Ecology. 57(5):890-899.

“Washington State.” Washington State Noxious Weed Control Board,