SCOTCH THISTLE

(Onopordum acanthium L.)

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COMMON NAMES:

Cotton thistle, heraldic thistle, Scotch cottonthistle

DESCRIPTION:

Scotch thistle is a biennial plant and the first year it produces a large rosette of spiny leaves. The plants typically germinate in the autumn and exist as rosettes throughout the first year forming a stout fleshy taproot. In the second year the plant can grow up to 12 feet tall. The upper leaves alternate coarsely lobed; the basal leaves may be up to 2 feet long and 1 foot wide and are covered with white wooly hairs. They have fine hairs that give the plant a grayish appearance. The massive main stem can be 4 inches wide at the base and is branched in the upper part. Flowers are globed shaped and are 1-2 inches in diameter. They are dark pink to lavender and produce in the summer. The flower buds form first at the tip of the stem and later at the tip of the axillary branches. They can appear singly or in groups of two or three on branch tips. Scotch thistle spreads rapidly reproducing only by seed. Seeds can remain viable in the soil for 7-20 years.

KEY FEATURES OF SCOTCH THISTLE:

Scotch thistle has a large rosette the very first year. This plant can grow up to 12 feet tall and will overtake any land that is disturbed in large clusters. The flower is very distinctive and with the color or pink to lavender. This plant is androgynous as it has both the pistil and stamens and sit above numerous, long stiff, spine-tipped bracts, all pointing outwards, and the lower ones are wider apart and pointing downwards. After flowering the ovary starts swelling and forms about 8,400-40,000 seeds per plant

HABITAT:

Scotch thistle likes to be in feed yards, pastures, rangeland, ravines, ponds, roadsides, disturbed sites, railroads, right-of-ways, yards, gardens and waste places.

CONTROL:

There are herbicides and other control methods that commonly control scotch thistle. For more information on these herbicides and other control methods contact the CCWP office.

OTHER FACTS:

Scotch thistle plants are frequently visited by butterflies. This plant has no poisoning effects. Scotch thistle can become so dense with stands that livestock cannot make it through.