Russian knapweed
Centaurea repens

Russian knapweed, also known as Russian cornflower, is a member of the thistle family. It can be identified by the presence of short, white hairs on its stems and leaves and its white to light rose, small flowers. These short white hairs - knap - give the plant its name. Flower heads are 3/8 to 1/2 inch (1 to 1.3 cm) across and are born in small clusters on branch tips. Seeds are light, almost straw-colored and shine like fresh, clean wheat straw. They are 1/8 inch (3.2 mm) long with one rounded and one pointed end. The plants are generally 2 to 3 feet (61 to 91 cm) tall with many branches. The hairy stems are tough, becoming hard and harsh as the plant matures. Russian knapweed has 2 distinct leaf types - upper and lower. The upper leaves are smaller, more narrow and have no lobes. The lower leaves are longer, wider and have indentations along their margins, resembling small dandelion leaves. The stems and leaves of this plant can be distinguished by a distinctive, bitter taste. Two unique characteristics of this species are the pale, egg-shaped flower head bracts and the dark brown, scaly roots. The roots, sometimes called "blackroot," are the most identifiable feature of Russian knapweed.