Cirsium occidentale

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Cirsium occidentale
Cobwebby 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.

Cirsium occidentale, with the common name cobwebby thistle, is a species of thistle in the Asteraceae family.

Distribution

The plant is native throughout California: in its mountain ranges, valleys, and the Mojave Desert; and in the Great Basin region in western Nevada, southern Oregon, and southwestern Idaho.[1][2]

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 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.[2] The petioles are winged and spiny and the leaves are toothed or edged with triangular lobes.

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.

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.[2]

Varieties

There are several varieties which differ from each other in range and form.[3] They include:

  • Cirsium occidentale var. californicum — endemic to California. [4]
  • Cirsium occidentale var. candidissimum — snowy thistle [5]
  • Cirsium occidentale var. compactum — compact cobwebby thistle; a short, clumpy plant endemic to California, which grows only along the coast of the San Francisco Bay Area and the Central Coast of California.[6]
  • Cirsium occidentale var. occidentale (Cirsium coulteri ) — endemic to California. [7]
  • Cirsium occidentale var. venustum [8]

References

  1. ↑ C.Michael Hogan ed. 2010. Cirsium occidentale. Encyclopedia of Life
  2. ↑ 2.0 2.1 2.2 U.C. Jepson; C. occidentale; 1993; accessed 3.20.2011
  3. ↑ Jepson Manual; Cirsium occidentale — 8 varieties list/treatment links; U.C. Berkeley; 1993 . accessed 3.20.2011
  4. ↑ USDA: Cirsium occidentale var. californicum
  5. ↑ USDA: Cirsium occidentale var. candidissimum
  6. ↑ U.C. Jepson; C. occidentale var. compactum; 1993; accessed 3.20.2011
  7. ↑ USDA: Cirsium occidentale var. occidentale
  8. ↑ USDA: Cirsium occidentale var. venustum

External links

Wikimedia Commons has media related to Cirsium occidentale.



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