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Canada thistle (Cimium arvense) is a non-native, deep-rooted perennial that spreads by seeds <br />and aggressive creeping, horizontal roots called rhizomes. Canada thistle can grow 2 to 4 feet in <br />height. The leaves are oblong, spiny, bright green, and slightly hairy on the undersurface. Unlike <br />other noxious biennial thistles which have a solitary flower at the end of each stem, Canada <br />thistle flowers occur in small clusters of 1 to 5 flowers. They are about 1 cm in diameter, tubular <br />shaped, and vary from white to purple in color. <br />Musk thistle (Carduus nutans) is a non-native biennial forb that reproduces solely by seed. A <br />biennial is a plant that completes its lifecycle within two years. During the first year of growth, <br />Musk thistle appears as a rosette in spring or fall. During the second year in mid to late spring, the <br />stem bolts, flowers, sets seed, and the plant dies. Musk thistle produces many flower heads. The <br />terminal, or tallest, shoots flower first, then lateral shoots develop in leaf axils. A robust plant <br />may produce 100 or more flowering heads. A prolific seed producer, Musk thistle can produce up <br />to 20,000 seeds per plant, only one-third being viable. Because Musk thistle reproduces solely <br />from seed, the key for successful management is to prevent seed production. <br />Cresson Project Weed Management Plan 10 <br />