Burke: Cirsium vulgare vs. Cirsium hookerianum

	Cirsium vulgare	Cirsium hookerianum
	bull thistle, common thistle	Hooker's thistle, white thistle
Habit	Stout biennial, 3-15 dm. tall, the stem conspicuously spiny-winged from the bases of the leaves and covered with stiff, blunt hairs.	Taprooted, short-lived perennial, the stem densely but loosely covered with long, soft hairs, 4-15 dm. tall, tapering above.
Leaves	Leaves pinnatifid, the largest again toothed or lobed; leaves covered with short, pointed hairs above and thinly white-woolly below.	Leaves with some loose, soft hairs above, thinly white-woolly below, narrowly lanceolate, toothed and moderately spiny.
Flowers	Heads several; involucre 2.5-4 cm. high, all its bracts spine-tipped; flowers all ligulate, purple or rarely white.	Heads clustered toward the top of the simple stem in a compact or elongated inflorescence; involucre 2-3 cm. high, strongly spider-webby, not much imbricate, the bracts all narrow and tapering, the middle and outer with a short, straight spine, the inner often twisted; flowers all tubular, creamy-white; receptacle densely bristly.
Fruits	Achenes less than 4 mm. long.

	Cirsium vulgare	Cirsium hookerianum
Flowering time	June-September	July-August
Habitat	Roadsides, fields, forest edge, ditches, balds, prairies, wastelots, and other disturbed, open areas.	Moist lowlands, open slopes and fields.
Distribution	Widely distributed on both sides of the Cascades crest in Washington; British Columbia to California, east to the Atlantic Coast. [WildflowerSearch map] [BONAP county map]	Occurring east of the Cascades crest in Washington; British Columbia to Washington, east to Alberta, Montana, and Wyoming. [WildflowerSearch map] [BONAP county map]
Origin	Introduced from Eurasia	Native
Conservation status	Not of concern	Not of concern
Sibling taxa	C. arvense, C. brevifolium, C. brevistylum, C. edule, C. flodmanii, C. hookerianum, C. inamoenum, C. remotifolium, C. scariosum, C. undulatum	C. arvense, C. brevifolium, C. brevistylum, C. edule, C. flodmanii, C. inamoenum, C. remotifolium, C. scariosum, C. undulatum, C. vulgare
Web links	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search	Local floras: BC, WA Local Web sites: Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search

Cirsium vulgare

Cirsium hookerianum

bull thistle, common thistle

Hooker's thistle, white thistle

Habit

Stout biennial, 3-15 dm. tall, the stem conspicuously spiny-winged from the bases of the leaves and covered with stiff, blunt hairs.

Taprooted, short-lived perennial, the stem densely but loosely covered with long, soft hairs, 4-15 dm. tall, tapering above.

Leaves

Leaves pinnatifid, the largest again toothed or lobed;

leaves covered with short, pointed hairs above and thinly white-woolly below.

Leaves with some loose, soft hairs above, thinly white-woolly below, narrowly lanceolate, toothed and moderately spiny.

Flowers

Heads several;

involucre 2.5-4 cm. high, all its bracts spine-tipped;

flowers all ligulate, purple or rarely white.

Heads clustered toward the top of the simple stem in a compact or elongated inflorescence;

involucre 2-3 cm. high, strongly spider-webby, not much imbricate, the bracts all narrow and tapering, the middle and outer with a short, straight spine, the inner often twisted;

flowers all tubular, creamy-white;

receptacle densely bristly.

Fruits

Achenes less than 4 mm. long.