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(Last Modified On 6/20/2013)
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(Last Modified On 6/20/2013)
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Genus
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Cirsium Miller,
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PlaceOfPublication
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Gard. Dict., abr. ed. 4. 1754.
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Description
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Acaulescent herb to 4 dm tall; stems simple to several from the base. Leaves alternate, usually lobed, spines distributed along the margins, frequently decurrent on the stem. Heads discoid; involucre multiseriate, the bracts usually imbricate, often spine-tipped, sometimes with a glutinous dorsal ridge; receptacle subconic, bristly; florets perfect, the corolla white to purple, tubular, 5-cleft, the anthers
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Habit
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herb
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Description
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appendaged, basally caudate with fringed auricles, the style with a thickened, often hairy ring below the branches, these connate except near the tip. Achenes oblong, somewhat flattened; pappus of plumose bristles.
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Note
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Cirsium has been confused with two Old World genera: Carduus and Cnicus. Carduus has barbellate pappus bristles while Cnicus has a 2-seriate pappus, the inner series being shorter than the outer. Cirsium can be differentiated by its uniseriate, plumose pappus. About 200 species of Cirsium are native to the Northern Hemisphere and about 50 species are native to temperate America. Besides the two species enumerated below, a third Cirsium species, C. vulgare (Savi) Airy-Shaw, has been seen from central Costa Rica (Taylor 4463B, NY). This additional taxon is an introduction from Europe, and in North America is widespread. Because of the weedy nature of C. vulgare, it is possible that further collecting will show that it occurs in Panama. Cirsium vulgare has decurrent leaves, as does C. mexicanum, but is easily distinguished by having reflexed involucral bracts and minute appressed spines on the upper leaf surfaces.
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Distribution
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About 200 species of Cirsium are native to the Northern Hemisphere and about 50 species are native to temperate America.
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Key
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a. Leaf bases decurrent, forming wings on the stem; involucre of mature heads 3-3.5 cm tall; outer rows of involucral bracts with a glutinous dorsal ridge ...... 1. C. mexicanum aa. Leaves clasping, not forming wings on the stem; involucre of mature heads 4.5-6 cm tall; none of the involucral bracts with a glutinous dorsal ridge ...... 2. C. subcoriaceum
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