Star thistle

Star thistle refers to a group of thistles in the Genus Centaurea of the Family Asteraceae. Some 350 species of herbaceous flowering plants belong to Centaurea, most native to the Old world. Some species are cultivated as garden ornamentals.

Species in this genus include:

• Centaurea calcitrapa L. – The Purple star thistle or Caltrop is a native of Europe. The Caltrop has spiny, pink-purple flower heads. It can be annual or biennial and has been naturalized in America. The common name "Caltrop" comes from the resemblance of the spiny flower head to the caltrop, an ancient instrument of war.

• Centaurea iberica Sprengle – A spiny Mediterranean species thought to be the "thistle" mentioned in Genesis

• Centaurea solstitialis L. – The Yellow star thistle, shown in the picture at right, is an annual that grows to a height of 1 to 2.5 feet. This plant is widely naturalized outside of Europe where it is native.

• Centaurea repens L. – Russian knapweed (also Turkestan thistle) is a perennial, native to southern Russia and Asia Minor to Atlai and Afganistan. It is a pernicious weed within parts of its native range as well as in places where it has been accidentally naturalized. The flower head is lilac in color and not armed with spines.

Bibliography

• Mabberley, D.J. 1987. The Plant Book. A portable dictionary of the higher plants. Cambridge University Press, Cambridge. 706 p. ISBN 0 521 34060 8.
• Robbins, W.W., M. K. Bellue, and W. S. Ball. 1970. Weeds of California. State of California, Dept. of Agriculture. 547 p.