St. Johnswort
Hypericum perforatum

St. Johnswort adult
This perennial grows one to three feet tall. Stems are rust colored and woody at the base.
St. Johnswort rosette
Weed Infestation
St Johnswort infestation
St. Johnswort was introduced from Europe. It invades areas with sandy or gravelly soils. Reproduction is by seeds and short runners. It contains a substance that is toxic (but rarely fatal) to white-haired animals causing them to develop skin irritations and often lose weight when exposed to sunlight. It is also a key ingredient of some popular dietary supplements.
St. Johnswort flower
The flowers are bright yellow with five petals.
St. Johnswort leaf
Leaves are characterized by prominent veins and transparent dots, visible when held up to light.