Scientific Family
Asteraceae
Synonyms
Onopordum acanthium ssp. acanthium
Other common names
cotton thistle
heraldic thistle
woolly thistle
Plant type
Forbs and Subshrubs
Origin
Introduced
Lifecycle
Biennial or annual
Similar species
Cirsium
Height
Often 8 feet or more
Riparian
No
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.
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.
Habitat
Disturbed sites, roadsides, grasslands, woodlands. Grows best in sandy, sandy clay and calcareous soils that are rich in ammonium salts.
Plant Community
Pinyon Juniper Woodlands
Montane Conifer Forest
Interior Chaparral
Grasslands
Disturbed Areas
Low elevation
3000
High elevation
10000
Flower Characteristics
Globe-shaped flower heads of disc flowers only, are 1 to 2 inches in diameter, bracts are spine-tipped.
Flower color
Purple to reddish
Flower shape
Daisy or dandelion-like
Tubular
No
First bloom month
June
Last bloom month
September
Flower clusters
None
Leaf and Stem Characteristics
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.
Leaf type
Simple
Leaf color
Grayish-green
Leaf shape
Round or oval
Leaf margin
Toothed
Leaves clasp
No
Leaf hairs
Leaves
Spines
Yes
Fruit and Seed Characteristics
Fruit type
Achene
Fruit color
Gray-black
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.