Spotted knapweed is a flowering plant that has become a harmful weed. The plant, native to Europe and western Asia, now grows widely in North America. It often invades grasslands, driving out native vegetation by spreading rapidly and by releasing into the soil a poisonous substance called cnicin << NY sihn >> . Spotted knapweed does not prevent soil erosion as well as native plants, and its spread may lead to erosion damage. Pasturelands overrun by the weed cannot easily support livestock, which prefer to eat the native plants.
Spotted knapweed has one or more slender, upright stems that stand about 1 to 3 feet (30 to 90 centimeters) tall. Its flowers usually range from pink to purple in color, though some are white. Black-tipped bracts (modified leaves) lie below the flowers’ petals, giving the blossoms a “spotted” appearance. Spotted knapweed can multiply rapidly because it produces more than 1,000 seeds per plant. Seeds may sprout from spring through fall. Those that begin to grow in the fall produce a group of leaves called a rosette before winter. The weed then remains inactive until spring, when it resumes growth. Spotted knapweed can live for two or more years.
People first brought the plant to North America in the late 1800’s. Since then, the weed has infested millions of acres or hectares of land there.
