Spotted knapweed is a pioneer species that readily invades open areas including pastures, open forests, prairies, meadows, and disturbed areas. The unpalatable herb displaces native vegetation, reducing the forage potential of open areas. It is able to invade undisturbed areas because it germinates and grows early in the spring. Another competitive advantage of Spotted knapweed is its phytotoxic effect on other plant species.
Spotted knapweed is native to Eastern Europe. It was introduced to North America in the late 1800s as a contaminant in alfalfa and clover seed or in ships' ballast. Today Spotted knapweed is a widespread invasive in the Lower Hudson Valley and is prohibited in New York State.
Spotted knapweed is found in disturbed sites, open forests, and in fields and meadows. It stems from a deep taproot, which allows it to acquire nutrients and water in poor soils.
Spotted knapweed is an herbaceous perennial or biennial. During its first year, it grows in a basal rosette with 6-8 inch leaves. Every year after that, it can grow to 3 feet tall, producing flowers at the tips of its branching stems. It produces purple to pink flowers during the early summer. Each plant produces about 1,000 shiny black seeds which form in erect, thin green pods that turn brown when mature. Mature seeds are dispersed by the wind.