Cirsium occidentale

Cirsium occidentale
Cobweb thistle
Flower head of Cirsium occidentale.
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Asterales
Family: Asteraceae
Tribe: Cynareae
Genus: Cirsium
Species: C. occidentale
Binomial name
Cirsium occidentale
(Nutt.) Jeps.
Synonyms[1]

Carduus occidentalis Nutt.

Wikimedia Commons has media related to Cirsium occidentale.

Cirsium occidentale, with the common name cobweb thistle or cobwebby thistle, is a North American species of thistle in the sunflower family.[2]

Distribution

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.[3][4][5]

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

Description

Plant form with blooms (Cirsium occidentale var. candidissimum).
Flower with seed head forming (Cirsium occidentale var. occidentale).

Cirsium occidentale is a biennial forming a taproot. It may be short or quite tall, forming low clumps or towering to heights approaching 3 metres (9.8 ft). 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 .5 metres (1.6 ft) in length.[4] The petioles are winged and spiny and the leaves are toothed or edged with triangular lobes.[6]

The inflorescence at the top of the whitish stem holds one to several flower heads. Each head is somewhat spherical, covered in large phyllaries with very long, spreading spines which are laced, often quite heavily, in fibers resembling cobwebs.[6]

The head is packed with disc florets which may be white to blood red to shades of purple. The largest flower heads exceed 8 centimetres (3.1 in) in diameter.[4] The heads do not open in synchrony, perhaps allowing for greater likelihood of being pollinated, as can be seen in the image of the plant in bloom at Fort Ord below.[6]

Plant in bloom (Cirsium occidentale growing on Trail 47 of Fort Ord National Monument).

Varieties

There are several varieties which differ from each other in range and form.[7] They include:

References

  1. ↑ The Plant List, Carduus occidentalis Nutt.
  2. ↑ Calflora taxon report,University of California, Cirsium occidentale (Nutt.) Jepson, Cobweb Thistle, western thistle
  3. ↑ C.Michael Hogan ed. 2010. Cirsium occidentale. Encyclopedia of Life
  4. 1 2 3 U.C. Jepson; C. occidentale; 1993; accessed 3.20.2011
  5. ↑ Biota of North America Program 2014 county distribution map
  6. 1 2 3 Flora of North America, Western thistle, Cirsium occidentale (Nuttall) Jepson
  7. ↑ Jepson Manual; Cirsium occidentale — 8 varieties list/treatment links; U.C. Berkeley; 1993 . accessed 3.20.2011
  8. ↑ United States Department of Agriculture Plants Profile: Cirsium occidentale var. californicum
  9. ↑ United States Department of Agriculture Plants Profile: Cirsium occidentale var. candidissimum
  10. ↑ University of California-Berkeley, Jepson Herbarium; C. occidentale var. compactum; 1993; accessed 3.20.2011
  11. ↑ United States Department of Agriculture Plants Profile: Cirsium occidentale var. occidentale
  12. ↑ United States Department of Agriculture Plants Profile: Cirsium occidentale var. venustum



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