Asia and Eastern Europe
Russian knapweed is a perennial forb, which reproduces both by seed and vegetatively through its extensive lateral root system. Plant stems are light green, ridged, branched, and typically only up to 3 ft (0.9 m) tall. Rosette leaves are up to 4 in (10 cm) long, gray-green, woolly, and lobed. Stem leaves are alternate and become smaller with smooth margins further up the stem. Flower heads are ½ in (1.3 cm) across with 15–35 pink or lavender florets. Bracts are triangular with a green base and papery tips and margins. The cream-colored seeds are topped by tufts of fine hairs that fall off at maturity.
Russian knapweed competes with other plants for limited resources and produces compounds that can inhibit the growth of some species. It can form dense infestations, displacing native plant species and reducing range, pasture, and crop production. The bitter taste of its seeds contaminate flour produced from Russian knapweed-infested grain crops. Similar to yellow starthistle (Centaurea solstitialis), Russian knapweed is toxic to horses, causing a chronic and potentially fatal neurological disorder known as “chewing disease”.
Bean, D.W., J. Littlefield, P. Weyl, S. Daly, and T. Collier. 2023. Russian Knapweed (Rhaponticum repens): History and Ecology in North America. In: R.L. Winston, Ed. Biological Control of Weeds in North America. North American Invasive Species Management Association, Milwaukee, WI. NAISMA-BCW- 2023-1-RUSSIAN KNAPWEED-P. https://bugwoodcloud.org/resource/files/28119.pdf