Russian knapweed (Centaurea repens
, previously referred to as Acroptilon repens
) is an upright, woody stem perennial. It emerges in the spring to form spreading branches and produces light pink to lavender flowers which bloom from June to September. It's leaves and stems are covered in gray hairs (knap). C. repens
is found in poorly drained and saline/alkaline soils with supplemental water sources such as rivers and streams.
is toxic to horses, however the exact toxins have not yet been defined. It is thought that repin, a type of sesquiterpene lactone is possibly responsible as it is known to be a neurotoxin. Ingestion of C. repens
causes equine parkinsonism (aka chewing disease)
in horses. The toxic effects of C. repens
are cumulative, which means that poisoning most often results from a build up of toxins in the body over a period of time. Horses must consume large quantities of fresh or dried C. repens
prior to reaching the toxic threshold. It is thought that horses must consume at least 60% of its body weight in C. repens
prior to clinical signs of toxicity appearing. For an average sized horse, this is 750lb (340 kg) of C. repens
. The disease is characterized by the impairment of the horse's facial muscles which inhibits the ability of the horse to bite off and chew food. Horses will often display continuous chewing motions with their mouth. The effects of C. repens
are irreversible and prove to be ultimately fatal to the horse.