Plant Image
Flower head
Watson Lake - Sue Smith

Yavapai County Native & Naturalized Plants

Onopordum acanthium - Scotch thistle

Synonyms: Onopordum acanthium ssp. acanthium
Other Common Names: cotton thistle, heraldic thistle, woolly thistle
Plant Form: Forb or Subshrub

Family: Asteraceae

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Flower head
Watson Lake
Sue Smith
Watson Lake
Sue Smith
Leaves - underside
Watson Lake
Sue Smith
Leaf - dense hairs
Watson Lake
Sue Smith
Plant - summer
Watson Lake
Sue Smith
Stems - spiny wings
Watson Lake
Sue Smith
Forb Plant Description

Origin: Introduced   Life Cycle: Biennial or annual   Similar Species: Cirsium
General Desc: Autumn seedlings behave as a biennial, producing a rosette with a taproot that may extend down 1 foot or more. Early in the second year, the plant bolts and flowers. Summer seedlings can behave as annuals. Naturalized.
Identification notes: Taprooted, primarily binennial; branches erect, appressed; leaves spiny hairy, basal; conspicuous spiny-winged stems; purple to reddish flowers of 18 to 50 ray flowers. Similar to Cirsium spp. distinguished by a fleshy and honey-combed receptacle.
Height: Often 8 feet or more


Habitat Description: Disturbed sites, roadsides, grasslands, woodlands. Grows best in sandy, sandy clay and calcareous soils that are rich in ammonium salts.
Plant Communities: Interior Chaparral, Semidesert Grasslands, Pinyon Juniper Woodland, Montane Conifer Forest, Disturbed Areas
Elevation: 3000 - 10000 feet

Flower Characteristics

Color: Purple to reddish     Shape: Daisy or dandelion-like not in clusters     Tubular: N     Flowering Period: Jun - Sep
Description: Globe-shaped flower heads of disc flowers only, are 1 to 2 inches in diameter, bracts are spine-tipped.

Leaf and Stem Characteristics

Leaf Color: Grayish-green     Leaf Type: Simple     Leaf Shape: Round or oval     Leaf Margin: Toothed     Leaf Attachment: Basal and alternate     Leaves Clasp: N
Hairs: Leaves     Spines: Y
Leaf Description: Stems have broad spiny wings of ribbon-like leaf material. Leaves are large, densely hairy, spiny and covered with dense hairs. Basal leaves may be up to 2 feet long and 1 foot wide, withering with age.

Fruit and Seed Characteristics

Fruit Color: Gray-black   
Fruit Type: Achene
Seed Notes: Seeds are smooth, slender, and tipped with slender, barbed bristles. A single plant can produce 8,400 to 40,000 seeds. Seeds are sensitive to light and only germinate when close to the surface.

  Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr #C
Prescott, AZ 86305
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Version 8.0  
Last Updated: Dec 13, 2022
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