MorphologyRead full entry
DescriptionMore info for the terms: allelopathy, forb, pappus
Russian knapweed is a nonnative, perennial, invasive forb that often forms dense, monotypic colonies from widely spreading horizontal roots. Roots are scaly and dark-brown to black in color, and can extend 14 square yards (12 mÂ²) radially, and up to 23 feet (7 m) deep within 2 growing seasons ([83,86] and sources therein). Records indicate that an infestation of Russian knapweed can survive 75+ years through its root system .
Russian knapweed shoot development originates from root-borne buds. A patch of Russian knapweed may have 9 to 27 shoots per square foot (100-300/mÂ²) . Russian knapweed stems are thin, erect and openly branched, standing up to 3 feet (0.9 m) tall. Rosette leaves are 2 to 4 inches (5-10 cm) long and 0.4 to 1 inch (1-2.5 cm) wide. Leaves grow smaller near the tops of the stems. Flowerheads arise terminally and are 0.25 to 0.5 inch (0.6 to 1.3 cm) in diameter. Russian knapweed seeds are achenes and are oblong, 2.1 to 2.4 mm in length by 0.6 to 0.7 mm in width. Seeds are covered with many fine hairs and have a pappus on the apex ([83,86] and sources therein).
Several allelopathic compounds have been isolated form Russian knapweed [29,71,72]. It is known that allelopathy plays an important role in Russian knapweed ecology and that these compounds can interfere with the growth of associated plants .