Cirsium genus --- aster subfamily 4
Anderson's thistle (Cirsium andersonii) -- in July -- Pacific Crest Trail, northern California red & pink
Canada thistle (Cirsium arvense) -- in June -- Coyote Ridge, Fort Collins Natural Area, CO red & pink
Canada thistle (Cirsium arvense) -- in July -- McMurry, a Fort Collins Natural Area, Larimer County, CO
Canada thistle (Cirsium arvense) -- in August -- Sportsman Lake Road, Wyoming
Canada thistle (Cirsium arvense) -- in August -- Tanglewood, Fort Collins Natural Area, CO
Canada thistle (Cirsium arvense) -- in August -- Arapaho National Wildlife Refuge, Jackson County, CO
Canada thistle (Cirsium arvense) -- in August -- Redwing Marsh, Fort Collins Natural Area, Larimer County, CO
Canada thistle (Cirsium arvense) with unlobed leaves -- in August -- Williams, Fort Collins Natural Area, Larimer County, CO
creamy thistle (Cirsium canescens) -- in June -- Pingree Park, Roosevelt National Forest, CO white & cream
fringed thistle (Cirsium clavatum) -- in July -- Red Feather Lakes, Roosevelt National Forest, CO white & cream
fringed thistle (Cirsium clavatum) -- in July -- Hermit Park Open Space, Larimer County, CO
fringed thistle (Cirsium clavatum) -- in July -- Buffalo Pass Road, Jackson County, CO
Osterhout's thistle (Cirsium clavatum var. osterhoutii) -- Shrine Pass Road, border of Eagle and Summit Counties, CO
Gray-green thistle (Cirsium cymosum var. canovirens) -- in June -- Steens Mountain WA, OR white & cream
Eaton's thistle (Cirsium eatonii) -- in September -- Trail Ridge Road, Rocky Mountain National Park, CO blue and purple
Steens Mountain thistle (Cirsium eatonii var. peckii) -- in June -- Steens Mountain Wilderness Area, OR red & pink
New Mexico thistle (Cirsium neomexicanum) -- in April -- Aguirre Springs NRA, NM blue and purple
yellowspine thistle (Cirsium ochrocentrum) -- in August -- Soapstone Prairie, Fort Collins Natural Area, CO red & pink
yellowspine thistle (Cirsium ochrocentrum) -- in August -- Hutton Lake National Wildlife Refuge, Albany County, Wyoming
Parry's thistle (Cirsium parryi) -- in July -- Herman Gulch, Clear Creek County, CO white & cream
meadow thistle (Cirsium scariosum) -- in July -- Shoshone National Forest, Fremont County, WY
meadow thistle (Cirsium scariosum) -- in July -- Lassen Volcanic National Park, CA white & cream
meadow thistle (Cirsium scariosum) -- in September -- Marshall Pass Road, Chaffee County, CO
mountain thistle (Cirsium scopulorum -- in July -- Georgia Pass, Park County, CO
mountain thistle (Cirsium scopulorum) -- in August -- Mount Evans, Arapaho National Forest, CO white & cream
mountain thistle (Cirsium scopulorum) -- in August -- Pikes Peak Area, CO
Tracy's thistle (Cirsium tracyi) -- in May -- Canyons of the Ancients National Monument, CO white & cream
wavy-leaved thistle (Cirsium undulatum) -- in July -- Pineridge Natural Area, Fort Collins, CO red & pink
bull thistle (Cirsium vulgare) -- in August -- Well Gulch Nature Trail, Lory State Park, CO red & pink
bull thistle (Cirsium vulgare) -- in May -- North Shields Ponds, Fort Collins Natural Area, CO
bull thistle (Cirsium vulgare) -- in August -- St. Vrain State Park, CO red & pink