Cirsium occidentale |
Cirsium discolor |
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cobwebby thistle, snowy thistle, Venus thistle, western thistle |
chardon discolore, field thistle |
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Habit | Biennials, 5–400 cm; taproots. | Biennials or sometimes perennials, 80–200 cm; taproots and often cluster of coarse fibrous roots, roots without tuberlike enlargements. | ||||||||||||||||||||||||
Stems | 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. |
single, erect, villous with septate trichomes, sometimes ± glabrate, distally ± tomentose; branches few–many, ascending. |
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Leaves | 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. |
blades oblanceolate to elliptic or ovate, 10–25(–50) × 1–13 (–25) cm, usually deeply divided more than halfway to midveins, proximal sometimes undivided, lobes linear-lanceolate, margins revolute, ascending, entire or spinulose to remotely few toothed or sharply lobed, main spines 1–5 mm, abaxial faces white-tomentose, adaxial faces green, villous with septate trichomes or glabrate; basal usually absent at flowering, winged-petiolate, bases tapered; principal cauline well distributed, gradually reduced, bases narrowed, sometimes weakly clasping, not decurrent; distal cauline well developed. |
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Peduncles | 1–30 cm. |
0–5 cm (not overtopped by crowded distal cauline leaves). |
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Involucres | 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. |
ovoid to broadly cylindric or campanulate, 2–3.5(–4) × 1.5–3 cm, thinly arachnoid. |
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Corollas | 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. |
pink to purple (white), 25–32 mm, tubes 12–16 mm, throats 7–10 mm, (noticeably wider than tubes), lobes 6–9 mm; style tips 4–6 mm. |
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Phyllaries | 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. |
in 10–12 series, strongly imbricate, greenish with subapical darker central zone, ovate (outer) to lanceolate (inner), abaxial faces with narrow glutinous ridge, outer and middle bodies appressed, margins entire, spines abruptly spreading to deflexed, slender, 3–9 mm; spines slender, 3–9 mm; apices of inner phyllaries spreading, narrow, flattened, finely serrulate. |
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Heads | 1–many in loose to tight clusters (barely raised above rosette in dwarf plants). |
1–many in corymbiform or paniculiform arrays. |
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Cypselae | ± brown, 5–6 mm, apical collars not differentiated; pappi 15–30 mm. |
tan to brownish, 4–5 mm, apical collars straw-colored, 0.5–75 mm; pappi 18–25 mm. |
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2n | = 20, 21, 22. |
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Cirsium occidentale |
Cirsium discolor |
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Phenology | Flowering summer–fall (Jun–Oct). | |||||||||||||||||||||||||
Habitat | Tallgrass prairies, deciduous woodlands, forest openings, disturbed sites, often in damp soil | |||||||||||||||||||||||||
Elevation | 5–800 m (0–2600 ft) | |||||||||||||||||||||||||
Distribution |
CA; NV; OR
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AL; AR; CT; DC; DE; GA; IA; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; NC; NE; NH; NY; OH; PA; RI; SC; SD; TN; VA; VT; WI; WV; MB; ON; QC; SK
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Discussion | Varieties 7 (7 in the flora). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Cirsium discolor is widespread in eastern North America from the prairies of southeastern Saskatchewan, western Minnesota, and Iowa south to northern Louisiana and east across southern Canada to the New England states and the southern Appalachians. It hybridizes with both C. altissimum (discussed thereunder) and C. muticum (G. B. Ownbey 1951b, 1964; W. L. Bloom 1977). Meiosis in first-generation hybrids between C. discolor and C. muticum is usually irregular (Bloom) and most pollen grains are infertile (Ownbey 1951b; Bloom). The presence of a small number of viable cypselae in heads of putative F1 hybrids (Ownbey 1951b) indicates that some F2 hybrids or backcrosses are formed. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 19, p. 137. | FNA vol. 19, p. 112. | ||||||||||||||||||||||||
Parent taxa | ||||||||||||||||||||||||||
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Synonyms | Carduus occidentalis | Cnicus discolor, Carduus discolor | ||||||||||||||||||||||||
Name authority | (Nuttall) Jepson: Fl. W. Calif., 509. (1901) | (Muhlenberg ex Willdenow) Sprengel: Syst. Veg. 3: 373. (1826) | ||||||||||||||||||||||||
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