slenderflower thistle

Asterales > Asteraceae > Carduus tenuiflorus W. Curtis
Synonym(s): Italian thistle, winged plumeless thistle

Slenderflower thistle is an herbaceous winter annual or biennial that invades disturbed areas. The most serious infestations occur in the Pacific coastal states, but slenderflower thistle also occurs sporadically in the eastern United States. Plants grow up to 6 ft. (1.8 m) tall with single or multiple spiny stems with wings arising from the base of the spines. Stem wings can be up to 0.4 in. (10 mm) wide. Leaves are deeply lobed and also very spiny. The small flower heads (less than 1 in. [2.5 cm] long) are slender, purple, and lack stalks. Flowering occurs from May to July. Slenderflower thistle invades pastures, old fields, vacant lots, and other disturbed areas. Its presence reduces the forage productivity of pastures. Slenderflower thistle is native to Europe and was recognized as a serious invader in the western United States as early as 1956.

Identification, Biology, Control and Management Resources

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Invasive Reference(s):

Check for most current lists.
  • California - Noxious Weed Law
  • California - Invasive Plant Inventory
  • Oregon - Noxious Weed Law
  • Washington - Noxious Weed Law

External Links

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USDA Forest Service Bugwood University of Georgia