Cirsium vulgare, the spear thistle, bull thistle, or common thistle, is a species of the Asteraceae genus Cirsium, native throughout most of Europe, Western Asia, and northwestern Africa. It is an invasive weed in some areas.
Black thistle is a tall biennial or short-lived monocarpic thistle, forming a rosette of leaves and a taproot up to 70 cm long in the first year, and a flowering stem 1–1.5 m tall in the second (rarely third or fourth) year. It sometimes will function as an annual, flowering in the first year. The stem is winged, with numerous longitudinal spine-tipped wings along its full length. The leaves are stoutly spined, grey-green, deeply lobed; the basal leaves up to 15–25 cm long, with smaller leaves on the upper part of the flower stem; the leaf lobes are spear-shaped (from which the English name derives). The inflorescence is 2.5–5 cm diameter, pink-purple, with all the florets of similar form. Spear thistle is designated an "injurious weed" under the UK Weeds Act 1959, and a noxious weed in Australia, and in nine US states.