Department Header For Noxious Weed Division
Yellowstone County, Montana
Noxious Weed
Weed Information Contact Department

St. Johnswort
(Hypericum perforatum L.)

Hypericum family - Clusiaceae


St Johnswort
Photo by Tom Whitson, Roy Reichenbach

Produced by Wyoming Weed & Pest Council in cooperation with Sandoz Crop Protection Corp.

St Johnswort Toxic

St Johnswort Resetta

St Johnswort Stem

St Johnswort Leaf

St Johnswort Bloom

St Johnswort Infestation

Toxcity: Humans and livestock.

Growth Habit: Perennial, erect, numerous branches.

Leaves: Opposite, attached directly to stem, 1 inch long, oblong, covered with transparent dots.

Stem: Woody at the base, 1 to 3 ft. tall, rust colored, with 2 ridges.

Flower: Yellow, 3/4 inch diameter, in fiat-topped clusters, 5 petals with numerous stamens.

Roots: Branched and deep, some shallow capable of sending up shoots.

Seeds: Small, shiny black, with rough texture in a round, pointed, three-part seed pod.

Reproduction: Seeds & new shoots.

Biological Controls: None used in Yellowstone County at this time.

Herbicides: None used in Yellowstone County at this time.

Caution: Contains a toxic substance which causes white-haired animals to become allergic to strong sunlight.


Video Supplied By Ravalli County Weed District