Cirsium griseum var. osterhoutii

(Gray Thistle)

_DSC1056%20copy

Cirsium griseum var. osterhoutii Hoosier Pass, Park Co. 5270

_DSC1056%20copy

Cirsium griseum var. ousterhoutii Hoosier Pass, Park Co. 1523

_DSC1056%20copy

Cirsium griseum var. ousterhoutii Hoosier Pass, Park Co. 1533

_DSC1056%20copy

Cirsium griseum var. ousterhoutii French Pass, Summit Co. 04949

_DSC1056%20copy

Cirsium griseum var. ousterhoutii French Pass, Summit Co. 04947

_DSC1056%20copy

Cirsium griseum var. ousterhoutii Hoosier Ridge, Summit Co.4752

_DSC1056%20copy

Cirsium griseum var. ousterhoutii Hoosier Pass, Park Co. 1501

_DSC1056%20copy

Cirsium griseum var. ousterhoutii Hoosier Ridge, Summit Co.4752

Scientific Name Cirsium griseum var. osterhoutii (Cirsium clavatum var. osterhoutii, Cirsium osterhoutii, Cirsium eatonii) USDA PLANTS Symbol CIOS
Common Name Osterhout's Thistle ITIS Taxonomic Serial No. 780836
Family Asteraceae (Sunflower) SEINet
Reference
n/a
Description Life zones and habitat: Montane to alpine (7000 to 12800 ft.); meadows and open areas in forests and alpine tundra.
Plant: Upright biennial/perennial, 8 to 40 inches tall, usually dark purple stems.
Leaves: Oblong to oblanceolate or elliptic 4 to 12 inches long, deeply pinnately-lobed, with spines at the tip of each lobe; smooth or slightly hairy above, smooth to woolly-hairy below; surfaces are green to purple and may have purple midvein; blades are decurrent (extending or wrapping down the stem) for 3/4-inch.
Inflorescence: Dense clusters of flower heads at stem tips or in leaf axils; central disk florets are white to pink, 5/8 to 1 inch long, and the styles are white with purple stripes; no ray flowers; involucre phyllaries are green to purple and densely hairy, often giving the flower head an overall white appearance; phyllaries have no rib along the back and have straight spines; outer phyllaries are longer than inner.
Bloom Period: July to September.
References: "Flora of Colorado" Second Edition by Jennifer Ackerfield, Thistle be a mess: Untangling the taxonomy of Cirsium (Cardueae: Compositae) in North America by Ackerfield, et al and Flora of North America.
Note: In the research document above by Ackerfield, et al, C. eatonii var. eriocephalum and C. clavatum var. osterhoutii become C. griseum var. osterhoutii.
BONAP Distribution Map


Map Color Key

Cirsium clavatum var. osterhoutii

Colorado Status:
Native

© Tom Lebsack 2024

Banner photo: Castilleja rhexifolia and a brewing storm over the San Juan Mountains