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2/26113 Canada thisUe-lnvasiw species : Minnesota DNR <br />Canada thistle ( Cirsium arvense) <br />Description: <br />Appearance: Perennial herbaceous plant, 2 -5' tall with slender grooved stems that <br />branch only at the top . It has male and female plants. <br />Leaves: Alternate, smooth, oblong, tapering, and directly attached to the stem, <br />deeply divided, with prickly margins. <br />Flowers: Numerous small purple flowers appear on top of the upper branched stems <br />between June and September. <br />Seeds: Small light brown seeds are tufted for dispersal by the wind. Seeds remain <br />viable in the soil for over 20 years. <br />Roots: Each plant has a fibrous taproot with wide spreading horizontal roots. Each <br />small section of root can form a new plant enabling the plant to spread vegetatively. <br />Ecological Thre at: <br />• Canada thistle invades natural areas such as prairies, savannas, glades and <br />dunes if some degree of disturbance already exists. It also invades wet areas <br />with fluctuating water levels such as streambanks, sedge meadows and wet <br />prairies. <br />• Once it has established itself it spreads quickly replacing native plants, <br />diminishing diversity. It grows in circular patches spreading vegetatively <br />through horizontal roots which can spread 10 -12' in one season. <br />• Canada thistle occurs throughout the northern U.S. from northern California to <br />Maine and southward to Virginia and in Canada. <br />• It has been declared a noxious weed in 43 states as one of the most tenacious <br />agricultural weeds. <br />• Canada thistle is a MDA Proh ibite d n oxio u s w eed < Co ntro ll ed Li st} in <br />Minnesota. <br />www.dnr .state.rm.us/invasi ws/ter restr ialplants/herbaceous/canadathi sUe.htrri 1/2