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slough thistle

Platte thistle, prairie thistle

Habit Annuals or biennials, (60–)100–300 cm; taprooted. Biennials or monocarpic perennials, 20–100 cm; taproots long.
Stems

usually 1, erect, stout, (hollow, 2–10 cm diam. at base), openly branched distally, thinly arachnoid, villous with jointed trichomes, at least proximally.

usually 1, erect, ± densely gray-tomentose with fine, non-septate trichomes;

branches 0 or few, usually above middle in distal 1/2, ascending.

Leaves

blades elliptic to broadly oblanceolate, 15–70 × 30–150+ cm, flat, pinnatifid 1/2–2/3 distance to midvein, larger usually with broad sinuses, lobes broad, few lobed or dentate, main spines 3–8 mm, abaxial faces gray-tomentose, adaxial thinly arachnoid-tomentose, sometimes midveins with jointed trichomes;

basal present or withered at flowering, winged-petiolate;

principal cauline sessile, progressively reduced distally, bases clasping or short-decurrent 1–2 cm;

distal cauline reduced, becoming bractlike, sometimes spinier than proximal.

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.

Peduncles

0–15 cm.

0–10 cm.

Involucres

ovoid to campanulate, 1.5–3 × 1.5–3 cm, ± glabrous.

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.

Corollas

pale rose-purple (white), 19–26 mm, tubes 9–12 mm, throats 4–6 mm, lobes 5–9 mm;

style tips 3.5–4.5 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.

Phyllaries

in 5–7 series, weakly unequal, dark green to brownish, lanceolate (outer) to linear (inner), abaxial faces without (or with very obscure) glutinous ridge;

outer and middle appressed or apices spreading, at least outer irregularly spiny-fringed, finely serrulate, spines slender, 3–5 mm;

apices of inner erect, abaxial faces gray-tomentose, ± twisted.

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.

Heads

1–several at branch tips, closely subtended by clustered leafy bracts or not, collectively forming open, corymbiform or paniculiform arrays.

1–10+, terminal on branches or in distal axils, in openly corymbiform to racemiform arrays.

Cypselae

dark brown, 5–5.5 mm, collars narrow, ± stramineous;

pappi 15–20 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.

2n

= 32.

= 34, 36.

Cirsium crassicaule

Cirsium canescens

Phenology Flowering spring (Apr–Jun). Flowering spring–summer (May–Aug).
Habitat Freshwater marshes, canal banks Sandy or gravelly soils in short-grass prairie, often in disturbed areas, mountain meadows, grassy slopes in montane coniferous forests
Elevation 5–100 m (0–300 ft) 1100–3800 m (3600–12500 ft)
Distribution
from FNA
CA
[BONAP county map]
from FNA
CA; CO; MO; MT; NE; NV; SD; WY
[WildflowerSearch map]
[BONAP county map]
Discussion

Cirsium crassicaule is known only from a few sites in the San Joaquin Valley. Some populations are threatened by habitat modification and development pressures.

(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.)

Source FNA vol. 19, p. 132. FNA vol. 19, p. 122.
Parent taxa Asteraceae > tribe Cardueae > Cirsium Asteraceae > tribe Cardueae > Cirsium
Sibling taxa
C. altissimum, C. andersonii, C. andrewsii, C. arizonicum, C. arvense, C. barnebyi, C. brevifolium, C. brevistylum, C. canescens, C. carolinianum, C. ciliolatum, C. clavatum, C. cymosum, C. discolor, C. douglasii, C. drummondii, C. eatonii, C. edule, C. engelmannii, C. flodmanii, C. foliosum, C. fontinale, C. grahamii, C. helenioides, C. hookerianum, C. horridulum, C. hydrophilum, C. inamoenum, C. joannae, C. kamtschaticum, C. lecontei, C. longistylum, C. mohavense, C. muticum, C. neomexicanum, C. nuttallii, C. occidentale, C. ochrocentrum, C. ownbeyi, C. palustre, C. parryi, C. perplexans, C. pitcheri, C. praeteriens, C. pulcherrimum, C. pumilum, C. quercetorum, C. remotifolium, C. repandum, C. rhothophilum, C. rydbergii, C. scariosum, C. texanum, C. tracyi, C. turneri, C. undulatum, C. vinaceum, C. virginianum, C. vulgare, C. wheeleri, C. wrightii
C. altissimum, C. andersonii, C. andrewsii, C. arizonicum, C. arvense, C. barnebyi, C. brevifolium, C. brevistylum, C. carolinianum, C. ciliolatum, C. clavatum, C. crassicaule, C. cymosum, C. discolor, C. douglasii, C. drummondii, C. eatonii, C. edule, C. engelmannii, C. flodmanii, C. foliosum, C. fontinale, C. grahamii, C. helenioides, C. hookerianum, C. horridulum, C. hydrophilum, C. inamoenum, C. joannae, C. kamtschaticum, C. lecontei, C. longistylum, C. mohavense, C. muticum, C. neomexicanum, C. nuttallii, C. occidentale, C. ochrocentrum, C. ownbeyi, C. palustre, C. parryi, C. perplexans, C. pitcheri, C. praeteriens, C. pulcherrimum, C. pumilum, C. quercetorum, C. remotifolium, C. repandum, C. rhothophilum, C. rydbergii, C. scariosum, C. texanum, C. tracyi, C. turneri, C. undulatum, C. vinaceum, C. virginianum, C. vulgare, C. wheeleri, C. wrightii
Synonyms Carduus crassicaulis C. nebraskense, C. plattense, C. nelsonii
Name authority (Greene) Jepson: Fl. W. Calif., 506. (1901) Nuttall: Trans. Amer. Philos. Soc., n. s. 7: 420. (1841)
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