SafePlants

Cirsium occidentale: Cobweb Thistle

Cirsium occidentale, commonly known as cobweb thistle or cobwebby thistle, is a striking North American thistle species belonging to the sunflower family.

Considerations for Pets

• The plant has spiny features.

Considerations for Children

• The plant has spiny features.

Taxonomy and Nomenclature

• Scientific Name: Cirsium occidentale (Nutt.) Jeps.
• Common Names: Cobweb thistle, cobwebby thistle, snowy thistle, Venus thistle.
• Family: Asteraceae (Sunflower family), also referred to as Compositae.
• Genus: Cirsium
• Varieties (Subordinate Taxa):
  • Cirsium occidentale var. californicum (A. Gray) Keil & C. Turner
  • Cirsium occidentale var. compactum
  • Cirsium occidentale var. venustum
  • Cirsium occidentale ssp. occidentale
• Synonyms/Aliases: California Thistle, Bigelow's Thistle

Distribution and Habitat

• Native to North America, specifically found throughout California deserts, mountains, and valleys.

Morphological Characteristics

• A PERENNIAL growing to 1 m (3ft 3in).
• Cobweb thistle is described as a tall, stout, leafy biennial growing from 2' to 5' tall.
• The involucres are large, globose, to 2" in diameter, and densely cobwebby.
• Classified as a forb/herb (a non-woody plant that is not a grass).
• Features red flowers and grayish stems and leaves.
• Flowers are hermaphrodite (have both male and female organs).

Ecological Role

• Mentioned in the context of biological control of exotic thistles.
• Serves as a nectar source for pollinators.

Additional Information

• Hardy to zone (UK) 9.

Resources

• Dave's Garden is a friendly community that shares tips and ideas for gardens, along with seeds and plants.
• Saint Mary's College of California
• Lady Bird Johnson Wildflower Center
• Discover Life
• Steven Foster Photos