Hooker's thistle (white thistle)
Asteraceae (Aster family)
Introduction to Vascular Plants
Species Information
General:
Biennial or short-lived perennial herb from a taproot; stems erect, thick, fleshy, ribbed, soft, sparsely long-hairy to short, curly-haired, 0.2-2.0 m tall.
Leaves:
Mainly basal, these narrowly oblanceolate, nearly entire or pinnately lobed to 1/2 the width of the blade, the segments triangular-lanceolate; stem leaves elliptic-oblong, clasping, up to 30 cm long and 3 cm wide, usually shallowly lobed, margins with a few, weak spines up to 5 mm long, lightly hairy above, densely woolly below.
Flowers:
Heads discoid, 1-6, in a terminal cluster; involucres short-bell-shaped, 2-3 cm tall; involucral bracts densely woolly, linear-lanceolate to lanceolate, not much graduated, middle and outer ones tapering to a slender 3-5 mm, yellow spine, inner ones abruptly sharp-pointed, unarmed, sometimes twisted at the tip; disk flowers white to creamy white, rarely pinkish, 20-26 mm long.
Fruits:
Achenes 5-6.5 mm long, brown with lighter parallel lines; pappus light yellow, 15-20 mm long, shorter than the corollas by 3-5 mm.
Illustration
If more than one illustration is available for a species (e.g., separate illustrations were provided for two subspecies) then links to the separate images will be provided below. Note that individual subspecies or varietal illustrations are not always available.
Illustration Source: The Illustrated Flora of British Columbia
Ecology
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 |
||
|
Avg |
Min |
Max |
|
| Elevation
(metres) |
1640 | 500 | 2563 |
| Slope
Gradient (%) |
41 | 0 | 100 |
|
Aspect (degrees) |
160 | 29 | 350 |
| Soil
Moisture Regime (SMR) [0 - very xeric; 4 - mesic; 8 - hydric] |
2 | 0 | 6 |
| Modal
Nutrient Regime
Class |
C | ||
| #
of field plots species was recorded in: |
121 | ||
| Modal
BEC Zone Class |
ESSF | ||
|
All BEC Zones (# of stations/zone) species was recorded in |
AT(10), BG(20), ESSF(70), ICH(2), IDF(14), MS(3) | ||
|
Source:
Klinkenberg 2013
|
|||
Habitat and Range
Moist to mesic roadsides, meadows and forest openings in the steppe and montane zones; frequent in S BC east of the Coast-Cascade Mountains; E to AB and S to ID, NW MT and WA.Status Information
Taxonomic Keys
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 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
4. Pappus of mature seeds exceeding the corollas by 1-10 mm.............. C. foliosum
5. Heads large; involucres 3-5 cm tall........... C. drummondii 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 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
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 Source: Illustrated Flora of British Columbia |