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Noxious Weeds


St. Johnswort/Goatweed/Klamath weed/Tipton weed (Hypericum perforatum L.)

St. Johnswort family (Clusiaceae) 

Composite photo of St. Johnswort

 

GROWTH HABIT:
This perennial native of Europestands 1 to 3 feet (30 to 90 cm) tall, is woody at the base, and has branches on the upper half of each stem. At the base are numerous leafy, barren shoots. It has creeping horizontal stems (stolons) that root at the nodes when they touch the ground. It has a fibrous root system. The flowering and fruiting period of Common St. Johnswort is from June through September.
LEAVES: 
The leaves are light green without stalks (sessile). They are oblong or long and narrow (linear) with an entire margin that rolls backward (revolute). The veins are prominent underneath and small transparent dots cover the blade. Leaves are 3/5 to 1 inch (15 to 25 mm) long and 1/12 to 1/6 inch (2 to 4 mm) wide. Short leafy branches are borne in the leaf axils. The seed leaves (cotyledons) are 1 1/2 times as long as they are broad, with three veins meeting in an imbedded gland at the tip. The first pair of true leaves are papery thin with fine granules on the surface (bloom). Later leaves of the seedlings have prominent, clear dots (punctate). The undersides of the leaf blades have about five elevated black glands at shallow indentations along the leaf margin.
FLOWERS:
The dense flat-topped flower cluster (cyme) is bright yellow. The outer, narrow (linear) green part of the flower (sepal) is lance shaped 1/6 to 1/5 inch (4 to 5 mm) long and gradually tapers to a short point (acuminate). The bright yellow flower is 3/5 to 1 inch (15 to 25 mm) wide and may have black dots on the edge of the five petals. There are numerous showy stamens above the petals.
SEEDS:
The seeds are borne in an oval-shaped, three-celled pod (capsule), 1/6 to 1/4 inch (4 to 6 mm) long, that breaks apart at maturity. The shiny, dark brown or black seeds are produced in large quantities. They are 1/40 to 1/35 inch (0.6 to 0.7 mm) long and are net veined (reticulate).
OTHER:
Common St. Johnswort is poisonous to livestock and difficult to eradicate, it is kept partially under check biologically by the Klamath weed beetle (Chrysolina quadrigenina [Suffrian]). It prefers dry, sandy or gravelly soils and often occurs in pastures, open woods, waste places, and along roadsides.
KEY CHARACTERS:
  • The leaf veins are prominent underneath and have small transparent dots cover the blade.
  • The seeds are borne in an oval-shaped, three-celled pod (capsule).
Distribution:Throughout agricultural areas - Inyo/Mono Counties