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Russian Knapweed (Acroptilon repens)  

Russian Knapweed rosettes.
Russian Knapweed rosettes.

Russian Knapweed is a bushy rhizomatous perennial, up to 4 feet tall. The first rosette leaves are oblanceolate to elliptic and not lobed and older rosette leaves are pinnately lobed. The heads are numerous terminating branches. Flowers are pink to purplish, about 1/2 inch in diameter and appear during the summer and fall.

Russian Knapweed is a deep-rooted long lived perennial. The roots may grow to a depth of 23 feet. Some stands have been in existence for 75 years. It forms dense colonies in cultivated fields, orchards, pastures, and roadsides.

A native to Eurasia, Russian Knapweed was introduced into North America in the late 1800s. Absent only from southeastern U.S., it has become widespread in other regions.

Russian Knapweed is toxic to horses and causes chewing disease. (From Wikipedia)

Russian Knapweed infestation in a pasture near the Snake River in eastern Idaho.
Russian Knapweed infestation in a pasture near the Snake River in eastern Idaho.

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