Cirsium_occidentale

<i>Cirsium occidentale</i>

Cirsium occidentale

Species of thistle

Cirsium occidentale, with the common name cobweb thistle or cobwebby thistle, is a North American species of thistle in the family Asteraceae.[3]

Quick Facts Cirsium occidentale, Conservation status ...

Description

Cirsium occidentale is a biennial plant forming a taproot. It may be short or quite tall, forming low clumps or towering to heights approaching 3 meters (10 feet). The leaves are dull gray-green to bright white due to a coating of hairs, and the most basal ones on large plants may be nearly 0.5 m (1+1⁄2 ft) in length.[4] The petioles are winged and spiny and the leaves are toothed or edged with triangular lobes.[5]

The inflorescence at the top of the whitish stem holds one to several flower heads. Each head is sphere-like, covered in large phyllaries with very long, spreading spines which are laced, often quite heavily, in fibers resembling cobwebs.[5]

The head is packed with disc florets which may be white to blood red to shades of purple. The largest flower heads exceed 8 centimeters (3 inches) in diameter.[4] The heads do not open in synchrony, perhaps allowing greater likelihood of being pollinated.[5]

Varieties

There are several varieties, which differ from each other in range and form:[4]

  • Cirsium occidentale var. californicum — California thistle[6]
  • Cirsium occidentale var. candidissimum — snowy thistle[7][8]
  • Cirsium occidentale var. compactum — compact cobwebby thistle; a short, clumpy California endemic that grows only along the coast of the San Francisco Bay Area and the Central Coast of California[9]
  • Cirsium occidentale var. coulteri — Coulter's thistle[10]
  • Cirsium occidentale var. lucianum — Cuesta Ridge thistle; a California endemic from the Santa Lucia Range[11]
  • Cirsium occidentale var. occidentale — cobwebby thistle[12]
  • Cirsium occidentale var. venustum[13][14]

Distribution and habitat

The plant is widespread and fairly common across most of California: in its mountain ranges, valleys, and the Mojave Desert; and in the western Great Basin region in western Nevada, southern Oregon, and southwestern Idaho.[15][4][16]

Unlike many introduced thistles, this native species is not a troublesome weed.

Ecology

It is a larval host to the California crescent, mylitta crescent, and the painted lady butterfly.[17]

  • California thistle
  • C. occidentale var. compactum blooming
  • C. occidentale
  • C. occidentale var. candidissimum
  • C. occidentale var. candidissimum flower
  • C. occidentale var. occidentale flower with seed head forming

References

  1. [1]
    "NatureServe Explorer". NatureServe Explorer. NatureServe. 2022. Retrieved 19 May 2022.
  2. [2]
    The Plant List, Carduus occidentalis Nutt.
  3. [3]
    Calflora taxon report, University of California, Cirsium occidentale (Nutt.) Jepson, Cobweb Thistle, western thistle
  4. [4]
    Jepson Flora Project (ed.). "Cirsium occidentale". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
  5. [5]
    Flora of North America, Western thistle, Cirsium occidentale (Nuttall) Jepson
  6. [6]
    Jepson Flora Project (ed.). "Cirsium occidentale var. californicum". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
  7. [7]
    "Plants Profile for Cirsium occidentale candidissimum (snowy thistle)". plants.usda.gov. Retrieved 2019-02-18.
  8. [8]
    Jepson Flora Project (ed.). "Cirsium occidentale var. candidissimum". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
  9. [9]
    Jepson Flora Project (ed.). "Cirsium occidentale var. compactum". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
  10. [10]
    Jepson Flora Project (ed.). "Cirsium occidentale var. coulteri". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
  11. [11]
    Jepson Flora Project (ed.). "Cirsium occidentale var. lucianum". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
  12. [12]
    Jepson Flora Project (ed.). "Cirsium occidentale var. occidentale". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
  13. [13]
    "Plants Profile for Cirsium occidentale venustum (cobwebby thistle)". plants.usda.gov. Retrieved 2019-02-18.
  14. [14]
    Jepson Flora Project (ed.). "Cirsium occidentale var. venustum". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
  15. [15]
    C.Michael Hogan ed. 2010. Cirsium occidentale. Encyclopedia of Life
  16. [16]
    Biota of North America Program 2014 county distribution map
  17. [17]
    The Xerces Society (2016), Gardening for Butterflies: How You Can Attract and Protect Beautiful, Beneficial Insects, Timber Press.
Share this article:

This article uses material from the Wikipedia article Cirsium_occidentale, and is written by contributors. Text is available under a CC BY-SA 4.0 International License; additional terms may apply. Images, videos and audio are available under their respective licenses.