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.

White/Cream Round Clusters | Blue/Purple Round Clusters