Plant Image
Flower head
Watson Lake - SS

Yavapai County Native & Naturalized Plants

Onopordum acanthium - Scotch thistle

Other Common Names: Scotch thistle, cotton thistle, heraldic thistle, woolly thistle
Plant Form: Forb

Family: Asteraceae

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

Origin: Introduced   Life Cycle: Biennial or annual
General Desc: Autumn seedling behaves 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 seedling behaves as annual.
Height: Often 8 feet or more


Habitat Description: Preferred habitats are natural areas, disturbed sites, roadsides, fields, agricultural areas, grasslands, riparian zones and scrub. Grows best in sandy, sandy clay and calcareous soils that are rich in ammonium salts.
Plant Communities: Desert Scrub, Interior Chaparral, Semidesert Grasslands, Pinyon Juniper Woodland, Disturbed Areas
Elevation: Below 5300 feet

Flower Characteristics

Color: Purple to reddish     Shape: Daisy or Dandelion-like not in clusters     Tubular: N     Flowering Period: Jun - Sep
Description: Globe-shaped flowerheads are 1 - 2 inches in diameter, bracts are spine-tipped.

Leaf and Stem Characteristics

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

Fruit and Seed Characteristics

Fruit Color: Whitish   
Fruit Type: Achene
Fruit Notes: Fruits are about 3/16 of an inch long and are tipped with slender bristles.
Seed Notes: Seeds are smooth, slender, and plumed. A single plant can produce 8,400 to 40,000 seeds.

  Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr #C
Prescott, AZ 86305
(928) 445-6590
Version 3.1  
Last Updated: June 15, 2013  
Content Questions/Comments: Email Jeff Schalau  
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