Hypericum perforatum (St Johns wort)

Kingdom Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Rosids
Order: Malpighiales
Family: Hypericaceae
Genus: Hypericum
Species: H. perforatum
Binomial name: Hypericum perforatum
Common name: St Johns Wort, Tipton's Weed, Chase-devil, or Klamath weed.

Hypericum perforatum is a yellow-flowering perennial herb indigenous to Europe, which has been introduced to many temperate areas of the world and grows wild in many meadows. In New Zealand, it can be found growing in tussock, grasslands, pasture, roadsides, waste places and prefers cooler areas. Its seeds are spread by birds, animals, on machinery & in hay. It is poisonous to livestock especially sheep causing photosensitivity sunlight intolerance).
St John's Wort is a plant with extensive, creeping rhizomes. Its stems <1.2m high are erect, branched in the upper section and are with reddish stems with 2 longitudinal ridges. It has opposing, stalkless, narrow, oblong leaves which are 12 mm long or slightly larger. The leaves are yellow-green in colour, with transparent dots throughout the tissue and occasionally with a few black dots on the lower surface. Leaves exhibit obvious translucent dots (oil-bearing glands) when held up to the light, giving them a ‘perforated’ appearance, hence the plant's Latin name.
The common name comes from its traditional flowering and harvesting on St John's day, 24 June in England. The genus name Hypericum is derived from the Greek words hyper (above) and eikon (picture), in reference to the traditional use of the plant to ward off evil, by hanging plants over a religious icon in the house during St John's day. The species name perforatum refers to the presence of small oil glands in the leaves that look like windows, which can be seen when they are held to the light.
Its flowers measure up to 2.5 cm across and have five petals, and are coloured bright yellow with conspicuous black dots. The flowers appear in broad cymes at the ends of the upper branches, between late spring and early to mid-summer. The sepals are pointed, with glandular dots in the tissue. There are many stamens, which are united at the base into three bundles. When flower buds (not the flowers themselves) or seed pods are crushed, a reddish/purple liquid is produced.