Thistle (5)

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 (6 feet), 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 noxious thistles. See more Thistles.

	Canada Thistle Cirsium arvense Family: Sunflower (Asteraceae) AKA: Creeping Thistle, Field Thistle Photo taken on: August 15, 2021 Location: Almont, CO Life Zones: Plains to montane Habitat: Disturbed soil An aggressive plant that grows 3 to 5 feet tall in large, dense colonies from a deep and wide-spreading root system. Leaves are very spiny and lobed with wavy edges. The many flower heads are purplish and ½" to ¾" across and less than 1" high. Bracts are pointed but do not have spines. Female flowers are flask-shaped and fragrant, male flowers are smaller and globe-shaped. Flora of North America reference. NOXIOUS
	Musk Thistle Carduus nutans Family: Sunflower (Asteraceae) AKA: Nodding Thistle, Bristle Thistle Photo taken on: July 20, 2009 Location: Wet Mountains, Eastern CO Life Zones: Plains to montane Habitat: Disturbed soil, roadsides Grows to 6 feet tall with long spiny leaves. Flower heads are up to 3" across with broad spiny bracts and are often nodding. Flora of North America reference. NOXIOUS
	New Mexico Thistle Cirsium neomexicanum Family: Sunflower (Asteraceae) AKA: Desert Thistle Photo taken on: May 15, 2009 Location: White Rock, NM Life Zones: Plains and foothills Habitat: Dry areas, roadsides Grows to several feet tall with a single grayish stem which branches towards the top. Leaves are grayish and deeply lobed. Bracts point downward and are cobwebby. Flower head is almost spherical and can be whitish. Blooms early. Flora of North America reference.
	Arizona Thistle Cirsium arizonicum var. bipinnatum Family: Sunflower (Asteraceae) AKA: Cainville Thistle, Four Corners Thistle Photo taken on: September 5, 2011 Location: Capulin Nat'l Monument, NM Life Zones: Foothills to montane Habitat: Rocky areas, woodlands Shorter than other thistle species with leaves divided into spine-tipped lobes that can be hairless or woolly. My identification is based on the egg shaped flower head and straight rather than rounded shape of the disk flowers. Flora of North America reference.
	Bull Thistle Cirsium vulgare Family: Sunflower (Asteraceae) AKA: Common Thistle, Spear Thistle Photo taken on: June 21, 2015 Location: CR 218, Rio Arriba, NM Life Zones: Plains and foothills Habitat: Disturbed areas, roadsides Grows over 7 feet tall with masses of long, intensely spiny leaves and many large, prickly flower heads that are to 2½" high. Flora of North America reference. NOXIOUS

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