Cirsium species

Click on the images below to see larger versions.

These thistle species are grouped under White flowers, because of the overall appearance of the flower heads, even though the disk florets range from yellow to purple to brown. The IDs are believed to be correct but these can be highly variable species. One of the identifiers is their habitat.

Scientific Name Cirsium canescens USDA PLANTS Symbol CICA11
Common Name Prairie Thistle ITIS Taxonomic Serial No. 36350
Family Asteraceae (Sunflower) SEINet
Reference
Click Here
Description Life zones and habitat: Plains to montane (3500 to 9500 ft.); sandy or gravelly soils on prairies and in disturbed areas, and in mountain meadows and coniferous forests.
Plant: Upright biennial, 16 to 32 inches tall.
Leaves: Oblong to elliptic or obovate leaves 3/4 to 2-3/8 inches wide and 4 to 10 inches long (upper leaves reduced), deeply pinnatifid, with spines at the tip of each lobe; blue-green in color; very hairy (cob-webby) above, densely woolly-hairy below.
Inflorescence: Open arrays (corymbs or racemes) of 1 to 10 or more flower heads; central disk florets are white or lavender-tinged, 3/4 to over 1 inch long; no ray flowers; involucre phyllaries with yellow upward- and outward-pointing spines on tips of outer row, with a whitish glutinous ridge below each tip.
Bloom Period: June to September.
References: "Flora of Colorado" by Jennifer Ackerfield, SEINet and "Thistles of Colorado" by Larimer County Weed Distict.
BONAP Distribution Map

Colorado Status:
Native
Scientific Name Cirsium eatonii USDA PLANTS Symbol CIEA
Common Name Eaton's Thistle, Mountaintop Thistle ITIS Taxonomic Serial No. 36365
Family Asteraceae (Sunflower) SEINet
Reference
Click Here
Description Life zones and habitat: Montane to alpine (9500 to 13000 ft.); open areas, common on rocky alpine slopes.
Plant: Upright biennial/perennial, 8 to 28+ inches tall.
Leaves: Oblong leaves 1/2 to 2 inches wide and 4 to 14 inches long, deeply pinnately-lobed, with spines at the tip of each lobe; smooth or slightly hairy above, woolly-hairy below.
Inflorescence: Spiny bracts around flower heads give white appearance to flowers; central disk florets lavender to purple 3/4 to 1 inch long; no ray flowers.
Bloom Period: July to September.
References: "Flora of Colorado" by Jennifer Ackerfield, and others.
BONAP Distribution Map

Colorado Status:
Native
Scientific Name Cirsium eatonii var. eriocephalum (Cirsium scopulorum) USDA PLANTS Symbol CISC3
Common Name Alpine Thistle, Mountain Thistle, Frosty Ball ITIS Taxonomic Serial No. 780840
Family Asteraceae (Sunflower) SEINet
Reference
Click Here
Description Life zones and habitat: Subalpine and alpine (10500 to 13500 ft.); open areas, meadows; windswept alpine ridges.
Plant: Upright perennial, 8 to 32 inches tall; stout, spiney stem.
Leaves: Basal and stem leaves, lanceolate 1 to 13 inches long, deeply pinnately-incised with lobes tipped by spines 1/2-inch long; smooth above, woolly-hairy below.
Inflorescence: Clusters of very hairy flower heads, often nodding; densely-hairy bracts with spines 3/8 to 3/4-inch long; white to yellow or light pink disk florets in the center; no ray flowers.
Bloom Period: July to September.
References: "Flora of Colorado" by Jennifer Ackerfield, "Guide to Colorado Wildflowers" by G.K. Guennel and SEINet.
BONAP Distribution Map

Colorado Status:
Native
Scientific Name Cirsium scariosum USDA PLANTS Symbol CISC2
Common Name Meadow Thistle ITIS Taxonomic Serial No. 36143
Family Asteraceae (Sunflower) SEINet
Reference
Click Here
Description Life zones and habitat: Montane to subalpine (7000 to 12500 ft.); moist open areas; meadows, along streams and roadsides.
Plant: Stemless or upright biennial/perennial, up to 40 inches tall; fleshy, thick single or multiple stalks branched from near base.
Leaves: Basal and stem leaves, linear to elliptic 4 to 16 inches long, very wavy, shallow or deeply pinnately-lobed with a broad central midstrip; sessile; smooth above and woolly-hairy below; spiney.
Inflorescence: Dense clusters of one to many flower heads; white to light lavender disk florets 3/4 to 1-3/8 inches long; pointed phyllaries with spines and teeth; no ray flowers.
Bloom Period: June to September.
References: "Flora of Colorado" by Jennifer Ackerfield and others.
BONAP Distribution Map

Colorado Status:
Native



© Tom Lebsack 2021