Cirsium palustre |
Cirsium occidentale |
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cirse ou chardon des marais, European Marsh thistle, European swamp or marsh thistle, European swamp thistle, marsh thistle |
cobwebby thistle, snowy thistle, Venus thistle, western thistle |
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Habit | Biennials or monocarpic perennials, 30–200(–300) cm; clusters of fibrous roots. | Biennials, 5–400 cm; taproots. | ||||||||||||||||||||||||
Stems | single, erect, villous to tomentose with jointed trichomes, distally tomentose with fine, unbranched trichomes; branches 0–few, ascending, (short). |
usually 1, thinly to densely gray- or white-tomentose, sometimes ± glabrate; branches few–many, usually from above mid or near base in compact, moundlike dwarf plants, ascending to spreading. |
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Leaves | blades narrowly elliptic to oblanceolate, 15–30+ × 3–10 cm, margins shallowly to very deeply pinnatifid, narrow lobes separated by broad sinuses, spiny-dentate to lobed, main spines 2–6 mm, abaxial villous to tomentose with jointed trichomes, sometimes also thinly tomentose with fine unbranched trichomes, adaxial faces villous with septate trichomes or glabrate; basal often present at flowering, petioles spiny-winged, bases tapered; cauline many, sessile, gradually reduced and becoming widely spaced above, bases long-decurrent with prominently spiny wings; distal cauline deeply pinnatifid with few-toothed spine-tipped lobes. |
blades oblong–elliptic to oblanceolate, 6–40 × 1.5–10+ cm, shallowly to deeply pinnatifid, lobes usually rigidly spreading, undivided or with 1–2 pairs of coarse teeth or lobes, main spines 5–15 mm, both faces gray- to white-tomentose, sometimes ± glabrate or adaxial faces green, thinly arachnoid-tomentose; basal sometimes present at flowering, petiolate or sessile and bases tapered, spiny-winged; principal cauline much reduced distally, sessile, bases decurrent or not, as spiny wings; distal much reduced, linear, ± bractlike. |
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Peduncles | 0–1 cm. |
1–30 cm. |
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Involucres | ovoid to campanulate, 1–1.5 × 0.8–1.3 cm, thinly cobwebby tomentose with fine unbranched trichomes. |
ovoid to spheric, 1.5–5 × 1.5–8 cm, arachnoid to ± loosely tomentose, often adjacent phyllaries connected by conspicuous arachnoid trichomes, sometimes glabrous or glabrate. |
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Corollas | lavender to purple (white), 11–13 mm, tubes 5–7 mm, throats 2–3 mm, lobes 3–4.5 mm; style tips 1.5–2 mm. |
white to lavender, pink, rose-purple, or red, 18–40 mm, tubes 8–18 mm, throats 5–7 mm, lobes 5–10 mm; style tips 4–5 mm. |
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Phyllaries | in 5–7 series, strongly imbricate, greenish, or with purplish tinge, lanceolate to ovate (outer) or linear-lanceolate (inner), margins thinly arachnoid-ciliate, abaxial faces with narrow glutinous ridge, outer and middle appressed, entire, apices acute, mucronate or spines erect or spreading, weak, 0.3–1 mm; apices of inner phyllaries purplish, linear-attenuate, scarious, flat. |
in 7–10 series, subequal to strongly imbricate, green or stramineous to purple-tinged, linear to narrowly lanceolate, abaxial faces without glutinous ridge; outer and mid bodies appressed, entire, apices deflexed to spreading or ascending, short-triangular to elongate, linear-acicular, spines spreading to reflexed, 1–10+ mm; apices of inner erect, often flexuous, flat. |
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Heads | few–many in dense clusters at branch tips. |
1–many in loose to tight clusters (barely raised above rosette in dwarf plants). |
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Cypselae | tan to stramineous, 2.5–3.5 mm, apical collars 0.1–0.2 mm, shiny; pappi 9–11 mm. |
± brown, 5–6 mm, apical collars not differentiated; pappi 15–30 mm. |
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2n | = 34. |
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Cirsium palustre |
Cirsium occidentale |
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Phenology | Flowering summer (Jul–Aug). | |||||||||||||||||||||||||
Habitat | Marshes, wet forests | |||||||||||||||||||||||||
Elevation | 10–800 m (0–2600 ft) | |||||||||||||||||||||||||
Distribution |
MA; MI; NH; NY; WI; BC; NF; NS; ON; QC; SPM; Europe [Introduced in North America]
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CA; NV; OR
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Discussion | Cirsium palustre is a noxious weed, native to Europe, that invasively spreads through wetland communities, forming impenetrable spiny stands as it displaces native species. The range of this pernicious weed in North America is rapidly expanding. It has the potential to spread into boreal forest areas across the continent; in Europe it grows nearly to the Arctic Circle. The rapid spread of C. palustre in Michigan (E. G. Voss 1972–1996, vol. 3) is indicative of its invasiveness. Spontaneous hybrids between C. palustre and C. arvense have been reported from England and other European countries (W. A. Sledge 1975) and can be expected wherever these species grow together in North America. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Varieties 7 (7 in the flora). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 19, p. 110. | FNA vol. 19, p. 137. | ||||||||||||||||||||||||
Parent taxa | Asteraceae > tribe Cardueae > Cirsium | Asteraceae > tribe Cardueae > Cirsium | ||||||||||||||||||||||||
Sibling taxa | ||||||||||||||||||||||||||
Subordinate taxa | ||||||||||||||||||||||||||
Synonyms | Carduus palustris | Carduus occidentalis | ||||||||||||||||||||||||
Name authority | (Linnaeus) Scopoli: Fl. Carniol. ed. 2, 2: 128. (1772) | (Nuttall) Jepson: Fl. W. Calif., 509. (1901) | ||||||||||||||||||||||||
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