The Mobius Arch in the Alabama Hills -- This rock arch perfectly frames Mount Whitney in the center opening.
BLM
U.S. DEPARTMENT OF THE INTERIOR
BUREAU OF LAND MANAGEMENT
Eastern Sierra Mountains Rock Climbing Strutting Sagegrouse Alabama Hills Cactus in Bloom
California
BLM>California>Bishop>Biological Resources>Invasive Species (Noxious Weeds)>Scotch Thistle
Print Page
Bishop Field Office

Noxious Weeds


Scotch thistle (Onopordum acanthium L.)

Sunflower family (Asteraceae) 

Composite photo of Scotch thistle

 

GROWTH HABIT:
Scotch thistle is a robust biennial to short-lived perennial plant native to Europe and western Asia. The mature plant is robust, and may grow 6.5 feet (2 m) tall. The stems are winged at the bases of the leaves and the wings extend well below the leaf blades. They may be as much as 2 inches (5 cm) broad and have numerous stiff horizontal spines.
LEAVES: 
The leaves are inversely lance shaped (oblanceolate), up to 12 inches (30 cm) long and 4 inches (10 cm) broad. The margins of the leaves are lobed and the lobes have sharp spines. The upper surface of the leaves is green; the underside is grayish. The lowest leaves on the main stem are oblong to egg shaped, 16 inches (40 cm) long and 8 inches (20 cm) broad, and without stalks. The thick seed leaves (cotyledons) are twice as long as they are broad and are united at the base to form a shallow cup. The first true leaves are three to four times as long as they are broad and their base extends more than halfway around the crown. Long hairs of unequal length form near the base of the plant. Short stiff hairs cover the leaf’s upper surface; the principal veins are visible on the undersides and margins of the leaves. Leaf stalks are not visible. Cottony, webbed hairs are matted around the developing bud; later, these disappear.
FLOWERS:
The flowering heads are somewhat globe shaped and 1 1/5 to 2 inches (3 to 5 cm) in diameter. They are borne singly at the tips of the branches, but there are many branches. The individual outer green, leaflike structures (bracts) on the flowering heads are lance shaped. The lower ones are pressed against one another (appressed); the upper ones are erect or spreading, tapering to a rigid spine. The flowers are reddish purple and exceed the greenish bracts.
FRUITS:
The one-seeded fruit (achene) is narrowly egg shaped, 1/5 to 1/4 inch (5 to 6 mm) long, somewhat flattened, and transversely wrinkled (rugulose). It is hairy, especially below the middle and is brownish gray at the base and almost black at the top, tipped with many short, slender bristles (pappus) 1/3 inch (8 mm) long.
OTHER:
It grows along roadsides, fencerows, ditchbanks, in waste areas and in pastures. It rarely infests cultivated annual crops.
KEY CHARACTERS:
  • The thick seed leaves (cotyledons) are twice as long as they are broad and are united at the base to form a shallow cup.
  • The flowers are reddish purple and exceed the greenish bracts.
Distribution:Common in Nevada