Russian knapweed (Rhaponticum repens)
Keys to ID:
- Pointed, papery tips of flower bracts.
- Roots are dark brown and have scale leaves
Identification:
- Lifecycle: Perennial
- Growth Form: Perennial
- Flower: Heads are urn-shaped, solitary, and composed of disk flowers. Floral bracts are broad, ovoid, entire, and greenish at the base with papery, finely hairy edges. The petals are pinkish-purple.
- Seeds/Fruit: Seeds are oval, grayish or ivory., with long white bristles at the tips when young.
- Leaves: Alternate; lower stem leaves are narrowly oblong to lance-shaped, and deeply lobed. The upper leaves are oblong, toothed, and become progressively smaller. Rosette leaves are lance-shaped, tapering at both ends, but broadest at the tip. Stems: Mature plants are between 18 and 36 inches tall. Stems are erect, thin, stiff, branched, and when young are covered with soft, short, grey hair.
- Roots: Black in color, with small-scale leaves.
- Propagation: primarily by aggressive root growth, but can be spread by seed, which is viable up to 8 years in soils. It can release chemical substances into the soils that inhibit the growth of competing vegetation (Belliston et al. 2004).
- Other: A variety of knapweed species are also listed in Salt Lake County as noxious weeds, but this species is common in the northwest part of the County and along the Jordan River.
Control:
Mech: Mowing repeatedly before plant bolts. Pulling and mowing may reduce seed production, but roots of plants will remain viable in the soils after these treatments.
Cautions:
Russian knapweed can cause severe allergic reaction in certain individuals. Care should be taken to limit exposure of skin to freshly cut or pulled plants and if any respiratory difficulty is experienced, the person should be monitored for a more severe reaction.