Cirsium clavatum |
Cirsium canescens |
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Fish Lake thistle, fringe thistle |
Platte thistle, prairie thistle |
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Habit | Biennials or monocarpic or polycarpic perennials, 20–100 cm; taproots sometimes with branched caudices. | Biennials or monocarpic perennials, 20–100 cm; taproots long. | ||||||||
Stems | 1–several, erect or ascending, glabrous or thinly arachnoid-tomentose; branches 0–10+, slender, usually arising in distal 1/2, ascending. |
usually 1, erect, ± densely gray-tomentose with fine, non-septate trichomes; branches 0 or few, usually above middle in distal 1/2, ascending. |
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Leaves | blades oblong to oblanceolate or elliptic, 5–40 × 3–11 cm, unlobed and merely spinulose-dentate or more commonly regularly deeply pinnatifid, lobes well separated to crowded, linear to triangular-ovate, ascending-spreading to retrorse, merely spinulose to coarsely dentate or proximally few-lobed, main spines 2–5(–7) mm, slender, abaxial faces green to gray, glabrous or thinly to densely arachnoid-tomentose, sometimes glabrate, often villous with septate trichomes along veins, adaxial green, glabrous; basal usually present at flowering, sessile or petiolate; principal cauline well distributed, proximal usually winged-petiolate, mid sessile, decurrent as spiny wings 1–3 cm; distal cauline ± reduced. |
blades oblong to elliptic or obovate, 10–25(–40) × 2–6(–12) cm, coarsely dentate or shallowly lobed to deeply pinnatifid, lobes well separated, triangular to linear or oblong, often revolute-margined, ascending to spreading, spinulose to spinose-dentate, main spines 2–3(–10) mm, faces gray-tomentose, more densely abaxially, sometimes glabrate adaxially; basal usually present at flowering, winged-petiolate; principal cauline progressively reduced distally, bases decurrent as spiny wings 1–5 cm, sometimes with expanded auricles; distal cauline usually much reduced, less lobed. |
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Peduncles | 0–30 cm. |
0–10 cm. |
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Involucres | ovoid to campanulate, 1.5–3 × 1–3 cm, glabrous to thinly arachnoid-tomentose and/or villous-ciliate, with long septate trichomes connecting adjacent phyllaries. |
hemispheric to broadly campanulate, usually truncate or indented at base, 3–4 × 2.5–4 cm in first-formed heads, often smaller (1.5–2 cm) in later ones, loosely arachnoid on phyllary margins or glabrate. |
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Corollas | creamy white to pale pinkish, 16–20 mm, tubes 6.5–9 mm, throats 4–7.5 mm, lobes 4–6 mm; style tips 3.5–5 mm. |
dull white or lavender-tinged, 20–35 mm, tubes 10–17 mm, throats 6–11 mm, lobes 4–9 mm; style tips 5–8 mm. |
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Phyllaries | in 5–6 series, imbricate or subequal, outer green or with maroon to dark brown subapical patch or appendage, linear to ovate, abaxial faces with narrow glutinous ridge that may be concealed by trichomes; outer and middle with bases appressed, apical appendages erect or ascending, ovate to linear-lanceolate or acicular, entire or spinulose to broadly expanded, scarious, and erose-dentate, apical appendages, spines erect or ascending, 1–5 mm, ± flattened; apices of inner sometimes flexuous or reflexed, narrow, flat, entire or ± expanded, scarious and lacerate-dentate. |
in 6–9 series, imbricate, ovate-lanceolate (outer) to linear-lanceolate (inner), abaxial faces with prominent glutinous ridge; bodies of outer and middle appressed, acute, spines ascending to spreading, 2–4(–8) mm; apices of inner expanded and flat, often twisted, scabrid-margined, and erose, spineless. |
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Heads | few–many, borne singly or clustered in corymbiform, paniculiform, or racemiform arrays at tips of main stem and branches, sometimes also in distal axils not closely subtended by clustered leafy bracts. |
1–10+, terminal on branches or in distal axils, in openly corymbiform to racemiform arrays. |
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Cypselae | tan to dark brown, 5–6 mm, apical collars not or scarcely differentiated; pappi 14–16 mm. |
light brown, 5–7 mm, sometimes with darker streaks, apical collar very narrow, lighter colored; pappi 18–30 mm, usually noticeably shorter than corolla. |
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2n | = 34, 36. |
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Cirsium clavatum |
Cirsium canescens |
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Phenology | Flowering spring–summer (May–Aug). | |||||||||
Habitat | Sandy or gravelly soils in short-grass prairie, often in disturbed areas, mountain meadows, grassy slopes in montane coniferous forests | |||||||||
Elevation | 1100–3800 m (3600–12500 ft) | |||||||||
Distribution |
CO; UT; WY; Central Rocky Mountains
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CA; CO; MO; MT; NE; NV; SD; WY
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Discussion | Varieties 3 (3 in the flora). Cirsium clavatum is a polymorphic and variable species. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Cirsium canescens grows in the northern Great Plains from eastern Montana and Wyoming to eastern Colorado and Nebraska; an upland race occurs in the Rocky Mountains of eastern Colorado. It has been reported from Iowa, North Dakota, and Ohio; I have not seen specimens from those states. It is adventive in northeastern California. Cirsium canescens hybridizes locally with C. scariosum and C. parryi. Further investigations may reveal that high-elevation forms of C. canescens from the mountains of Colorado are worthy of taxonomic recognition. These plants flower later than the low elevation forms of the Great Plains and occur in rather different ecologic conditions, but I have found no features that readily distinguish them. Populations of C. canescens have been particularly affected by the seedhead weevil Rhinocyllus conicus, introduced to North America to control weedy species of Carduus (S. M. Louda et al. 1997; Louda 1998). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 19, p. 126. | FNA vol. 19, p. 122. | ||||||||
Parent taxa | ||||||||||
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Synonyms | Cnicus clavatus | C. nebraskense, C. plattense, C. nelsonii | ||||||||
Name authority | (M. E. Jones) Petrak: Beih. Bot. Centralbl. 35(2): 310. (1917) | Nuttall: Trans. Amer. Philos. Soc., n. s. 7: 420. (1841) | ||||||||
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