Weed of the Week

July 10th 2006

Scotch Thistle, Onopordum acanthium, L.

                             

 

Characteristics:

Family: Asteraceae (Sunflower)

Origin: Europe and eastern Asia

Description:

• Biennial
• Forms a rosette in the first season of growth
• Bolts, flowers, and sets seed in the second year of growth
• Reproduces only by seed

Stems:

• Multiple stems, erect and thick, with many spiny winged branches
• Grows up to 12 feet tall

Flowers:

• Rose to violet in color
• 1 inch or more in diameter, bracts are tipped with spines
• Bloom occurs June-August
• Seeds are 3/16 inch, attached to stiff bristles

Leaves:

• Basal leaves are long (2 ft) and broad (1 ft) and densely covered with hair
• Color is grayish to light green
• Upper leaves are alternate, and deeply lobed

Location:

     Scotch Thistle is often found along roadways and railways, in waste areas and on rangeland.  If left unmanaged, dense stands will form.  Scotch Thistle is most easily distinguishable from other thistles by it's enormous size and grayish appearance.  While Musk Thistle flower heads often nod from the stem and are disk shaped, Scotch Thistle flower heads point up and are rounder, more tear-drop shaped.

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