Yellow Starthistle (Centaurea solstitialis)

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Annual, sometimes biennial, growing to 2 m tall. Taproots grow vigorously early in the season to soil depths of 1 m or more. Basal leaves are 6 - 7 cm long and deeply lobed. Upper leaves are short 1 to 2.5 cm and narrow, with few lobes. Foliage is grayish- to bluish-green, densely covered with fine white cottony hairs that hide thick stiff hairs and glands. Yellow corollas mostly 13-20 mm long. Central spine of main phyllaries 10-25 mm long, stout, yellowish to straw-colored throughout. Lateral spines typically 2-3 pairs at the base of the central spine. Outer ring of achenes dull dark brown, often speckled with tan, lack pappus bristles, often remain in heads. Inner achenes glossy, gray or tan to mottled cream-colored and tan, with slender white pappus bristles 2-5 mm long. Heads shed the central spines, but tightly retain a ball of dense fuzzy gray hairs (chaff) on the receptacle. Chewing disease develops in horses that have eaten yellow starthistle. This disease affects horse’s nervous system and is usually fatal.

Key Identifiers
  • Surfaces densely covered with fine cottony hairs
  • Leaf bases extend down the stems and give stems a winged appearance
  • Flowerheads are spiny, solitary on stem tips, and consist of numerous yellow disk flowers
  • Phyllaries are palmately spined, with one long central spine and 2 or more pairs of short lateral spines

Steve Dewey, Utah State University,

Richard Old, XID Services, Inc.,
Location in Canada
Alberta, Manitoba, Ontario and Saskatchewan have all reported sightings according to Flora of North America. But none presently known in Alberta.

Resources Similar species
Malta starthistle (Centaurea melitensis) has smaller seed heads with reduced spines which are branched at base.
Purple starthistle (Centaurea calcitrapa) upper leaves do not form a wing down stem and flowers are purple.

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Yellow Starthistle (Centaurea solstitialis) - Current Document
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For more information about the content of this document, contact Chris Neeser.
This document is maintained by Shelley Barkley.
This information published to the web on April 10, 2012.
Last Reviewed/Revised on August 21, 2018.