Biology:Cirsium occidentale

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Short description: Species of thistle

Cirsium occidentale
Cirsium occidentale.jpg
Flower head of Cirsium occidentale

Vulnerable (NatureServe)[1]
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Asterales
Family: Asteraceae
Genus: Cirsium
Species:
C. occidentale
Binomial name
Cirsium occidentale
(Nutt.) Jeps.
Synonyms[2]

Cirsium coulteri

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

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]

Gallery

  • 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. ↑ "NatureServe Explorer". NatureServe. 2022. https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.143708. 
  2. ↑ The Plant List, Carduus occidentalis Nutt.
  3. ↑ Calflora taxon report, University of California, Cirsium occidentale (Nutt.) Jepson, Cobweb Thistle, western thistle
  4. ↑ 4.0 4.1 4.2 4.3 Jepson Flora Project, ed., "Cirsium occidentale", Jepson eFlora, The Jepson Herbarium, University of California, Berkeley, http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=2209 
  5. ↑ 5.0 5.1 5.2 Flora of North America, Western thistle, Cirsium occidentale (Nuttall) Jepson
  6. ↑ Jepson Flora Project, ed., "Cirsium occidentale var. californicum", Jepson eFlora, The Jepson Herbarium, University of California, Berkeley, http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=77401 
  7. ↑ "Plants Profile for Cirsium occidentale candidissimum (snowy thistle)". https://plants.usda.gov/core/profile?symbol=CIOCC. 
  8. ↑ Jepson Flora Project, ed., "Cirsium occidentale var. candidissimum", Jepson eFlora, The Jepson Herbarium, University of California, Berkeley, http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=56556 
  9. ↑ Jepson Flora Project, ed., "Cirsium occidentale var. compactum", Jepson eFlora, The Jepson Herbarium, University of California, Berkeley, http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=7068 
  10. ↑ Jepson Flora Project, ed., "Cirsium occidentale var. coulteri", Jepson eFlora, The Jepson Herbarium, University of California, Berkeley, http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=81843 
  11. ↑ Jepson Flora Project, ed., "Cirsium occidentale var. lucianum", Jepson eFlora, The Jepson Herbarium, University of California, Berkeley, http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=81502 
  12. ↑ Jepson Flora Project, ed., "Cirsium occidentale var. occidentale", Jepson eFlora, The Jepson Herbarium, University of California, Berkeley, http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=7069 
  13. ↑ "Plants Profile for Cirsium occidentale venustum (cobwebby thistle)". https://plants.usda.gov/core/profile?symbol=CIOCV. 
  14. ↑ Jepson Flora Project, ed., "Cirsium occidentale var. venustum", Jepson eFlora, The Jepson Herbarium, University of California, Berkeley, http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=56557 
  15. ↑ C.Michael Hogan ed. 2010. Cirsium occidentale. Encyclopedia of Life
  16. ↑ Biota of North America Program 2014 county distribution map
  17. ↑ The Xerces Society (2016), Gardening for Butterflies: How You Can Attract and Protect Beautiful, Beneficial Insects, Timber Press.

External links


Wikidata ☰ Q19848754 entry



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