Thistle (7)
There are many thistles, both native and introduced, in the area. All have spiny leaves. Flower heads have disk flowers only. Colors range from creamy white to yellow to lavender to purple, even in the same species. They are difficult to differentiate. Flora of North America explains the complexity. There are 20 native thistle species in Colorado. How do you tell a native thistle from a noxious thistle? Generally, if the stand of thistles is very dense or very tall (6ft), it is usually noxious. If you are above timberline and see a thistle, it’s probably native. Native thistles tend to be short, often white, and are usually only found as individual plants or in very small groups of 2-4 plants. Here are a few thistles, identification not guaranteed. See also purple Thistles.
Eaton's Thistle
Cirsium eatonii
Family:
Sunflower (Asteraceae)
AKA:
Mountaintop Thistle
Photo taken on:
August 5, 2006
Location:
Snodgrass, GV, CO
Life Zones:
Montane to subalpine
Habitat:
Meadows, open slopes
Grows to 4ft tall, erect with few branches. Flowers are off-white to lavender. Spines on bracts are not bent backwards. Leaves narrow and regularly toothed with spines.
Flora of North America reference.
Colorado Thistle
Cirsium coloradense (C. scariosum var. coloradense)
Family:
Sunflower (Asteraceae)
AKA:
Elk Thistle, Meadow Thistle
Photo taken on:
July 19, 2007
Location:
Crested Butte Mountain, CO
Life Zones:
Montane to subalpine
Habitat:
Moist areas, mountain meadows
Grows to 4ft tall or in a rosette with stemless flower heads. Leaves and stem are light green. Flowers are white to lavender and grow in leaf axils. Bracts have spines that stick out at 90°.
Flora of North America reference.
Meadow Thistle
Cirsium scariosum
Family:
Sunflower (Asteraceae)
AKA:
Elk Thistle
Photo taken on:
August 9, 2008
Location:
Cottonwood Pass, CO
Life Zones:
Montane to alpine
Habitat:
Meadows
Stout growing to 2ft with thick succulent leaves distributed evenly up the single stems. Flower heads are whitish to pale pink in clusters at the top of the stem.
Flora of North America reference.
American Thistle
Cirsium centaureae
Family:
Sunflower (Asteraceae)
AKA:
Fringed Thistle
Photo taken on:
July 17, 2010
Location:
Brush Creek, GV, CO
Life Zones:
Montane to subalpine
Habitat:
Forests and meadows
Grows to 3ft tall with medium-sized flower heads. Flowers are white to cream with purple stripes. Bracts are fringed on the edges and do not have spines.
Mountain Thistle
Cirsium scopulorum (C. eatonii var. hesperium)
Family:
Sunflower (Asteraceae)
AKA:
Alpine Thistle, Frosty Ball, Woolly Thistle
Photo taken on:
July 2, 2010
Location:
Cottonwood Pass, CO
Life Zones:
Subalpine to alpine
Habitat:
Rocky slopes, trail-sides
A very spiny, robust plant growing to 2ft with white, cobwebby hairs around a cluster of drooping, creamy white
to purplish flower heads. 
Mountain Thistle
Cirsium scopulorum (C. eatonii var. hesperium)
Photo taken on:
August 15, 2015
Location:
East Ridge, Mt. Yale, CO
This splendid specimen was photographed by Gary & Marilyn Hollenbaugh who wondered if it belonged in the Little Shop of Horrors. It was a wet spring in the mountains.
Wavyleaf Thistle
Cirsium undulatum var. tracyi
Family:
Sunflower (Asteraceae)
AKA:
Tracy's Thistle
Photo taken on:
June 30, 2008
Location:
Almont, CO
Life Zones:
Foothills to montane
Habitat:
Dry openings, sagebrush
Flowers are solitary, white to lavender and larger than Canada Thistle.
Flora of North America reference.
Parry's Thistle
Cirsium parryi
Family:
Sunflower (Asteraceae)
AKA:
Photo taken on:
July 17, 2010
Location:
Brush Creek, GV, CO
Life Zones:
Montane
Habitat:
Moist meadows and woods
Grows 3 to 6ft tall with undivided, wavy edged leaves. Flower heads are greenish-yellow with cobwebby, pointed phyllaries.
Flora of North America reference.