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Platte thistle, prairie thistle

Tracy's thistle

Habit Biennials or monocarpic perennials, 20–100 cm; taproots long. Perennials, 50–200+ cm; tap-rooted.
Stems

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

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

1–several, erect or ascending, thinly gray-tomentose or ± glabrate;

branches few to many, ascending.

Leaves

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.

blades elliptic to oblong, 8–40 × 1–12 cm, margins weakly to strongly undulate, spinose-dentate or shallowly to deeply lobed, lobes ascending to spreading, ± triangular, mostly well separated, spinulose and coarsely dentate or cleft into 2–3 lanceolate to triangular, often entire-margined, spine-tipped divisions, main spines 2.5–7+ mm, abaxial faces densely gray-tomentose, adaxial thinly tomentose;

basal sometimes present at flowering, winged-petiolate;

principal cauline becoming sessile and progressively reduced distally, widest at bases, bases ± auriculate-clasping to short-decurrent;

distal cauline reduced, often spinier.

Peduncles

0–10 cm.

0–10+ cm.

Involucres

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.

ovoid to hemispheric or broadly campanulate, 2–3 × 1.7–3.5 cm, loosely arachnoid on phyllary margins or glabrate.

Corollas

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.

white to lavender or pink-purple, 23–30 mm, tubes 9–14 mm, throats 5.5–10.5 mm, lobes 5.5–9.5 mm;

style tips 4–7 mm.

Phyllaries

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.

in 6–10 series, imbricate, ovate to lanceolate (outer) to linear-lanceolate (inner), margins entire, abaxial faces with prominent glutinous ridge;

outer and middle appressed, spines spreading, slender to stout, 2–6 mm;

apices of inner often flexuous, narrow, flat, ± entire, spineless or tipped with weak spines.

Heads

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

1–many, terminal on branches and often in leaf axils, in leafy, ± corymbiform arrays.

Cypselae

light brown, 5–7 mm, sometimes with darker streaks, apical collar very narrow, lighter colored;

pappi 18–30 mm, usually noticeably shorter than corolla.

light to dark brown, 6–7 mm, apical collars colored like body or rarely yellowish, narrow;

pappi 20–23 mm, usually noticeably shorter than corolla.

2n

= 34, 36.

= 24.

Cirsium canescens

Cirsium tracyi

Phenology Flowering spring–summer (May–Aug). Flowering late spring–summer (Jun–Aug).
Habitat Sandy or gravelly soils in short-grass prairie, often in disturbed areas, mountain meadows, grassy slopes in montane coniferous forests Dry slopes, sagebrush deserts, pinyon-juniper woodlands, openings in montane coniferous forests, often in disturbed areas
Elevation 1100–3800 m (3600–12500 ft) 1400–2900 m (4600–9500 ft)
Distribution
from FNA
CA; CO; MO; MT; NE; NV; SD; WY
[WildflowerSearch map]
[BONAP county map]
from FNA
CO; NM; UT
[WildflowerSearch map]
[BONAP county map]
Discussion

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.)

Cirsium tracyi occurs from eastern Utah and western Colorado south in the Colorado Plateau and southern Rocky Mountains to northwestern New Mexico. Large-headed plants of Cirsium tracyi and small-headed individuals of C. undulatum are sometimes difficult to distinguish. P. L. Barlow-Irick (unpubl.) found that although there is much overlap in floral measurements of C. tracyi and C. undulatum, the means for some of these characters are statistically significant. Corolla lobes of C. tracyi, for instance, average about 7 mm and those of C. undulatum about 10 mm. The species differ in chromosome number as well.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 19, p. 122. FNA vol. 19, p. 121.
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. 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
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. 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. turneri, C. undulatum, C. vinaceum, C. virginianum, C. vulgare, C. wheeleri, C. wrightii
Synonyms C. nebraskense, C. plattense, C. nelsonii Carduus tracyi, C. acuatum, C. floccosum, C. undulatus var. tracyi
Name authority Nuttall: Trans. Amer. Philos. Soc., n. s. 7: 420. (1841) (Rydberg) Petrak: Beih. Bot. Centralbl. 35(2): 424. (1917)
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