Cirsium vulgare
Cirsium scariosum
bull or common or spear thistle, bull thistle, chardon vulgaire ou lancéolé, common thistle, gros chardon, piqueux, spear thistle
chardon écailleux, dinnerplate thistle, elk thistle, meadow thistle
1–many, erect or ascending, branches few–many, ascending, villous with septate trichomes.
absent, or with crowded branches from near base, or simple and erect, often fleshy and thickened, glabrous to thinly gray- tomentose, often villous with septate trichomes.
blades oblong-lanceolate to obovate, 15–40 × 6–15 cm, margins plane or revolute, coarsely 1–2-pinnatifid with rigidly divergent lobes, sometimes merely spinose-dentate, lobes triangular to lanceolate, entire to spiny-dentate, main spines 2–10 mm, abaxial faces gray-tomentose, villous with septate trichomes along veins, adaxial green, covered with short appressed bristlelike spines, sometimes tomentose when young;
basal present or absent at flowering, petioles winged, bases tapered;
principal cauline winged-petiolate, mid and distal becoming sessile, well distributed or not, progressively reduced distally, at least distal decurrent as long spiny wings;
distal cauline often more deeply lobed than proximal, main lobes rigidly spiny, margins spinulose, otherwise entire.
blades linear to elliptic, 5–20 × 3–7 cm, plane to strongly undulate, unlobed or shallowly to deeply pinnatifid, lobes linear-lanceolate to broadly triangular, closely spaced, spreading, spinose-dentate or lobed, main spines slender to stout, 2–15+ mm, abaxial faces glabrous or thinly to densely tomentose, ± villous with septate trichomes along the veins, glabrate or trichomes persistent, adaxial thinly arachnoid tomentose and soon glabrescent;
basal often present at flowering, sessile or winged-petiolate;
cauline many in caulescent forms, reduced distally or not, winged-petiolate or distal sessile;
distal often well developed, similar to proximal, sometimes much narrower and bractlike.
1–6 cm.
0–10 cm, leafy-bracted.
hemispheric to campanulate, 3–4 × 2–4 cm, loosely arachnoid-tomentose.
ovoid to hemispheric, 2–4 × 1.5–6 cm, loosely arachnoid on phyllary margins or glabrate.
purple (rarely white), 25–35 mm, tubes 18–25 mm, throats 5–6 mm, lobes 5–7 mm;
style tips 3.5–6 mm.
white or pale lavender to purple, 20–40 mm, tubes 7–24 mm, throats 4–12 mm (noticeably larger than tubes), lobes 4–10 mm;
style tips 3.5–8 mm.
in 10–12 series, strongly imbricate, linear-lanceolate (outer) to linear (inner), outer and middle appressed, (bases stramineous), margins entire, abaxial faces without glutinous ridge, apices radiating, greenish, spines 2–5 mm;
apices of inner phyllaries flat, serrulate to minutely erose.
in 5–10 series, imbricate, ovate or lanceolate (outer) to linear or linear-lanceolate (inner), margins (outer) entire or scarious-fringed, abaxial faces without glutinous ridge;
outer and mid appressed, spines erect to spreading 0.5–13 mm;
apices of mid and inner narrowed and scabro-denticulate or with expanded, erose-dentate tips, spineless or tipped with flattened spines.
few–many in corymbiform or paniculiform arrays.
1–many, erect, borne singly or often densely crowded in spiciform, racemiform, or subcapitate arrays, especially in acaulescent or short-caulescent plants, often closely subtended by distalmost leaves.
light brown with darker streaks, 3–4.5 mm, apical collar not differentiated;
pappi 20–30 mm.
light to dark brown, 4–6.5 mm, apical collars usually colored like body;
pappi 17–35 mm, white to tan.
= 68.
= 34, 36.
Cirsium vulgare
Cirsium scariosum
Native to Eurasia, Cirsium vulgare is the only thistle in North America with bristlelike spines borne on the adaxial leaf faces. These structures are variously described in the literature as trichomes (“spreading hirsute,” “scabrous-hispid,” “coarsely hispid,” “rigid, rather pungent setae,” “prickly-hairy”), prickles, or spines (“setose-spinulose,” “appressed and dense spines”). My examination of cleared leaves of C. vulgare indicated that these structures are not epidermal outgrowths (trichomes or prickles) but emerge from fine veinlets within the tissues of the leaf. As such, they are properly treated as spines.
Bull thistle is a noxious weed that has invaded disturbed habitats across the continent. Distasteful to livestock, it can increase in heavily grazed pastures. It occurs in a wide variety of habitats.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Varieties 8 (8 in the flora).
Cirsium scariosum is a widely distributed complex of intergrading races distributed from southwestern Canada to northwestern Mexico. These plants range from acaulescent rosettes with a tight cluster of sessile heads to tall, erect, unbranched plants, or moundlike, more or less openly branched herbs. Acaulescent and caulescent plants sometimes occur in the same population.
Members of this complex have been variously treated in the past. F. Petrak (1917) recognized ten species plus several subspecies for the taxa I am treating here as C. scariosum (in the broad sense). In floras, the names C. drummondii and C. foliosum have been widely misapplied to these plants (R. J. Moore and C. Frankton 1964). The latter two species, while clearly related to C. scariosum, have a range restricted mostly to Canada. Moore and Frankton (1967) attempted to bring order to the complex and recognized four species for plants that I include here in C. scariosum: C. acaulescens, C. congdonii, C. coloradense, and C. scariosum in the restricted sense. Moore and Frankton substituted the prior name C. tioganum for C. acaulescens. Unfortunately they did not extend their study widely enough and did not include some members of the complex in their investigations. S. L. Welsh (1982) proposed C. scariosum var. thorneae from Utah and lumped the various species recognized by Moore and Frankton within a highly polymorphic var. scariosum. After consulting with A. Cronquist and studying his manuscript treatment of Cirsium for the Intermountain Flora, D. J. Keil and C. E. Turner (1993) also accepted a broadly construed C. scariosum. Cronquist (1994) treated C. scariosum as an extremely variable species that included the four species recognized by Moore and Frankton plus the variety proposed by Welsh. Cronquist chose to not recognize infraspecific taxa.
In the present treatment I have examined these plants from a biogeographic perspective with the goal of discerning regional patterns of variation. The large number of specimens available has allowed me to examine distributional patterns in relation to the topography and biogeographic history of the regions where this species occurs. My field studies also have provided me with observations that help to explain some of the anomalous specimens represented in herbaria. Although the variation within and between populations is sometimes amazing, more-or-less differentiated geographic races can be discerned. Because of the extraordinary and overlapping patterns of variation across the range of Cirsium scariosum, the following key to varieties should be regarded as at best an approximation.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Plants acaulescent (occasional short-caulescent individuals sometimes present in a population) | → 2 |
1. Plants caulescent (occasional acaulescent individuals sometimes present in a population) | → 4 |
2. Corollas pink to purple; Sierra Nevada of w Nevada and e California to San Bernardino Mountains of s California | var. congdonii |
2. Corollas white to faintly pink-or lilac-tinged; widespread | → 3 |
3. Abaxial leaf faces usually gray-tomentose; widespread, Colorado to s Oregon, n California | var. americanum |
3. Abaxial leaf faces usually green, glabrous or glabrate; s. California | var. citrinum |
4. Larger leaf spines 1–3 cm | Cirsium scariosum var. thorneae |
4. Larger leaf spines usually shorter | → 5 |
5. Corollas purple | → 6 |
5. Corollas white to faintly pink- or lilac-tinged | → 7 |
6. Corolla lobes 5.5–8 mm; sw. Idaho, n Nevada, se Oregon | var. toiyabense |
6. Corolla lobes 3.5–6 mm; e Oregon to sw Montana | var. scariosum |
7. Stems usually proximally branched, plants often forming low, rounded mound; heads usually borne on short to ± elongate lateral branches; corollas 26–36 mm | → 8 |
7. Stems usually erect, proximally unbranched; heads usually sessile or short-pedunculate in subcapitate to spiciform or racemiform arrays, usually closely subtended by numerous distal leaves; corollas 20–29 mm | → 9 |
8. Apices of inner phyllaries acuminate and entire or rarely toothed; s California | var. citrinum |
8. Apices of inner phyllaries usually expanded as a scarious, erose-toothed appendage; ne California, se Oregon | var. robustum |
9. Heads usually ± tightly clustered at stem tips, closely subtended and often overtopped by crowded distal leaves; distal leaves ± thin, usually fringed with numerous weak spines, often ± unpigmented proximally or tinged pink to purplish | var. scariosum |
9. Heads usually in ± leafy, racemiform arrays, usually subtended by ± reduced, bractlike distal leaves; distal leaves firm, strongly spiny, usually green throughout | var. coloradense |
- Local floras:
BC, 
CA, 
OR, 
WA - Local Web sites: CalFlora, CalPhotos,
Flora NW, 
Go Botany, 
IL Wildflowers, 
KS Wildflowers, 
LA Plants, 
MD Biodiversity, 
MI Flora, 
MN Wildflowers, 
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WildflowerSearch
iNaturalist (observations)
USDA Plants Database- LBJ Wildflower Center
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- Local floras: BC, CA, OR, WA
- Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria, Turner Photog.
- WildflowerSearch
- iNaturalist (observations)
- USDA Plants Database
- LBJ Wildflower Center
- SEINet
- Plants of the World Online
- Encyclopedia of Life
- Wikipedia
- Google Image Search
