E-Flora BC: Electronic Atlas of the Flora of British Columbia

Cirsium arvense (L.) Scop.
Canada thistle
Asteraceae (Aster family)

Introduction to Vascular Plants

© Doug Skilton  Email the photographer   (Photo ID #2687)

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Distribution of Cirsium arvense
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Species Information

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General:
Perennial herb from deep, wide-spreading roots and creeping underground stems; stems erect, glabrous, branched above, 0.3-2.0 m tall.
Leaves:
Basal leaves soon deciduous; stem leaves alternate, lance-shaped on the lower stem, becoming broader upwards, up to 20 cm long and 7 cm wide, irregularly lobed, spiny-toothed, glabrous or green above, densely white-hairy beneath.
Flowers:
Heads discoid, unisexual (composed of either male or female flowers) numerous, small, solitary at the ends of branches in an open inflorescence; involucres 1-2 (rarely 2.5) cm tall; involucral bracts glabrous or slightly cobwebby, outer ones egg-shaped, awl-tipped, inner ones progressively longer and lanceolate, unarmed; disk flowers pink-purple, rarely white, female ones 23-26 mm long, the male ones 12-14 mm long.
Fruits:
Achenes 2.5-4 mm long; pappus tawny, exceeding the corollas.

Source: The Illustrated Flora of British Columbia

Habitat / Range

Mesic to dry roadsides, fields and disturbed areas in the lowland, steppe and montane zones; common in W, SC and NE BC; introduced from Eurasia.

Source: The Illustrated Flora of British Columbia

Additional Notes

Canada thistle is our only species of thistle with separate male and female plants (Moore 1979). Moore (1979) indicates that it was introduced to North America "very early in the colonial period, probably in the 17th century". A single seedling can produce a large patch through vegetative propagation (Moore 1979). This species is listed as one of the top fourteen species of concern by the Coastal Invasive Plant Committee, for more information visit their web site.

Reference

Moore, R. J. Cirsium arvense (L.) Scop. In: Mulligan, Gerald A. 1979. The Biology of Canadian Weeds: Contributions 1-32. Biosystematics Research Institute, Ottawa.

Illustrated Flora of British Columbia TAXONOMIC KEY TO CIRSIUM

1. Heads small; involucres 1-2 (rarely 2.5) cm tall; plants introduced.

2. Stems distinctly spiny-winged; plants with perfect flowers C. palustre

2. Stems not conspicuously spiny-winged; plants partly of male and female flowers C. arvense

1. Heads large; involucres more than 2 cm tall; plants native (except C. vulgare).

3. Leaves bristly-spiny above, stems distinctly spiny-winged C. vulgare

3. Leaves cobwebby to loosely woolly-hairy, woolly or nearly glabrous above, stems not spiny-winged.

4. Pappus of mature seeds exceeding the corollas by 1-10 mm C. foliosum

4. Pappus of mature seeds shorter than the corollas.

5. Heads large; involucres 3-5 cm tall C. drummondii

5. Heads small; involucres less than 3 cm tall.

6. Outer involucral bracts more than 2 mm wide at base, slightly if at all hairy and if so, then mainly marginal.

7. Outer involucral bracts strongly glandular; lowermost leaves deeply pinnately lobed more than 1/2 the width of the blade C. undulatum

7. Outer involucral bracts without glands; lowermost leaves shallowly pinnately lobed to 1/2 or less the width of the blade C. scariosum

6. Outer involucral bracts less than 2 mm wide at base, densely cobwebby.

8. Corollas white or creamy-white, rarely pinkish; involucral bracts greenish C. hookerianum

8. Corollas purplish-red to purplish-pink; outer involucral bracts purplish.

9. Styles exceeding the corollas by at least 3 mm; achenes 5-6.5 mm long; leaves usually lobed more than 1/2 the width of the blade C. edule

9. Styles nearly equal to or exceeding the corollas by only 1.5 mm; achenes 4-4.5 mm long; leaves usually lobed less than 1/2 the width of the blade C. brevistylum

Ecology

Ecological Framework for Cirsium arvense

The table below shows the species-specific information calculated from
original data (BEC database) provided by the BC Ministry of Forests and Range.
(Updated August, 2013)

Site Information
Value / Class

Minimum

Average

Maximum

Elevation (metres) 0 795 2200
Slope Gradient (%) 0 11 90
Aspect (degrees)
[0 - N; 90 - E; 180 - S; 270 - W]
0 199 360
Soil Moisture Regime (SMR)
[0 - very xeric; 4 - mesic;
8 - hydric]
1 4 8
Modal Nutrient Regime
Class
C
Number of field plots
 species was recorded in:
308
Modal BEC Zone Class
CWH
All BEC Zones (# of stations/zone) species was recorded in: BG(12), CDF(2), CWH(77), ESSF(18), ICH(36), IDF(75), MS(29), PP(15), SBS(23), SWB(3)

Climate

The climate type for this species, as reported in the: "British Columbia plant species codes and selected attributes. Version 6 Database" (Meidinger et al. 2008), is not evaluated, unknown or variable.

Synonyms and Alternate Names

Breea arvensis Less.
Breea incana (Gmel.) W.A. Weber
Carduus arvensis (L.) Robson
Cirsium arvense var. argenteum (Vest) Fiori
Cirsium arvense var. horridum Wimmer & Grab.
Cirsium arvense var. horridum Wimm. & Grab.
Cirsium arvense var. integrifolium Wimmer & Grab.
Cirsium arvense var. mite Wimmer & Grab.
Cirsium arvense var. vestitum Wimmer & Grab.
Cirsium incanum (Gmel.) Fisch.
Cirsium setosum (Willd.) Bess. ex Bieb.
Serratula arvensis L.

Taxonomic and Nomenclatural Links

Additional Photo Sources

Related Databases

General References