Whitehall Biological Weed Control Project: Russian Knapweed

Russian knapweed (Rhaponticum repens) has blue green lobed leaves and pink to purple flowers. In the spring it grows a basal rosette (a ring of leaves located at the base of the plant) and then bolts (rapidly shoots up stems that flower) as the summer progresses. The flowers are very similar to spotted knapweed and can be difficult to differentiate. One of the key differences between these species is spotted knapweed has bracts on the flower buds with dark colored tips whereas Russian knapweed's bracts are smooth and opaque, without any spines. These bracts are located underneath the blooms an...