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 (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 noxious thistles. See more Thistles.

Cirsium arvense

Canada Thistle
Cirsium arvense

Family: Sunflower (Asteraceae)
AKA: Creeping Thistle
Photo taken on: August 4, 2005
Location: Almont, CO
Life Zones: Plains to montane
Habitat: Disturbed soil

Grows to 6ft in dense patches. Leaves are very spiny and lobed. Flower heads are ½" across.

Flora of North America reference.

NOXIOUS

Carduus nutans

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 6ft 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

Cirsium neomexicanum

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.

Cirsium neomexicanum

Flora of North America reference.

Cirsium arizonicum var. bipinnatum

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.

Cirsium vulgare

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 7ft tall with masses of long, intensely spiny leaves and many large, prickly flower heads that are to 2½" high.

Cirsium vulgare

Flora of North America reference.

NOXIOUS

Blue/Purple Round Clusters | Pink Round Clusters