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yellow thistle

Scientific Name: Cirsium horridulum var. vittatum

Family: Asteraceae

Category: Dicot

Growth: Forb/herb

Duration: Annual, Biennial

Other Names:

       

Yellow Starthistle (Centaurea solstitialis)

Yellow starthistle is an invasive annual plant known for its distinctive yellow flowers and spiny seedheads. It poses a significant challenge in many regions due to its aggressive growth and ability to outcompete native vegetation.

Considerations for Pets

  • The seedheads have spines that can attach to animal fur.

Considerations for Children

  • The plant has thorns, especially around the flower heads.

Common Names

  • Yellow starthistle
  • Geeldissel
  • Golden star thistle
  • St. Barnaby's thistle
  • Yellow centaury
  • Yellow cockspur

Taxonomy and Nomenclature

  • Scientific Name: Centaurea solstitialis
  • Family: Asteraceae (also referred to as N.O. Composite)
  • Related To: Knapweeds and other starthistles
  • Synonym: St. Barnaby's Thistle

Distribution and Habitat

  • Native Range: Mediterranean Basin region, Africa, temperate Asia, and Eurasia (Balkan-Asia Minor, the Middle East, and south-central Europe).
  • Introduced Range: Western United States (introduced as a seed contaminant).
  • Habitat: Disturbed areas such as roadsides, abandoned fields, and waste areas.
  • Specific Locations: California foothills, Yosemite National Park.

Ecological Role

  • Yellow starthistle is considered an invasive species.
  • It forms highly competitive and often impenetrable stands.
  • It is a problematic weed in Yosemite National Park.

Morphological Characteristics

  • Growth Habit: Long-lived winter annual, occasionally biennial.
  • Height: Can grow from 0.25 to 3 feet (0.07 to 0.9 meters) in height.
  • Foliage: Leaves near the base are petiolate and dissected, 2-6 in length.
  • Color: Silvery-green when young, becoming gray-green later in the season. The plant has a blue-green coloration.
  • Flowers: Yellow with thorns underneath.

Interactions with Other Organisms

  • Flowers provide nectar for honey bees.
  • The seedheads attach to animal fur via spines.
  • The Yellow Starthistle Hairy Weevil (Eustenopus villosus) is used as a biological control agent; the adults feed on the flowers, and the larvae consume the seed heads.

Further Information

  • University of California guidelines for control of Yellow Starthistle.
  • Center for Invasive Species and Ecosystem Health.
  • UC IPM Pest Management Guidelines: Yellow Starthistle.