Cirsium griseum var. osterhoutii
(Gray Thistle)
Cirsium griseum var. osterhoutii Hoosier Pass, Park Co. 5270
Cirsium griseum var. ousterhoutii Hoosier Pass, Park Co. 1523
Cirsium griseum var. ousterhoutii Hoosier Pass, Park Co. 1533
Cirsium griseum var. ousterhoutii French Pass, Summit Co. 04949
Cirsium griseum var. ousterhoutii French Pass, Summit Co. 04947
Cirsium griseum var. ousterhoutii Hoosier Ridge, Summit Co.4752
Cirsium griseum var. ousterhoutii Hoosier Pass, Park Co. 1501
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