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]
Cirsium occidentale | |
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Flower head of Cirsium occidentale | |
Scientific classification | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Clade: | Angiosperms |
Clade: | Eudicots |
Clade: | Asterids |
Order: | Asterales |
Family: | Asteraceae |
Genus: | Cirsium |
Species: | C. occidentale |
Binomial name | |
Cirsium occidentale | |
Synonyms[1] | |
Cirsium coulteri |
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 thistles, this native species is not a troublesome weed.
Description
Cirsium occidentale is a biennial forming a taproot. It may be short or quite tall, forming low clumps or towering to heights approaching 3 meters (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 0.5 meters (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 sphere-like, 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 centimeters (3.1 in) in diameter.[4] The heads do not open in synchrony, perhaps allowing greater likelihood of being pollinated.[6]
Ecology
It is a larval host to the California crescent, mylitta crescent, and the painted lady butterfly.[7]
Varieties
There are several varieties, which differ from each other in range and form:[4]
- Cirsium occidentale var. californicum — California thistle[8]
- Cirsium occidentale var. candidissimum — snowy thistle[9][10]
- 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[11]
- Cirsium occidentale var. coulteri — Coulter's thistle[12]
- Cirsium occidentale var. lucianum — Cuesta Ridge thistle; a California endemic from the Santa Lucia Range[13]
- Cirsium occidentale var. occidentale — cobwebby thistle[14]
- Cirsium occidentale var. venustum[15][16]
Gallery
- Cirsium occidentale
- California thistle
- Cirsium occidentale var. candidissimum
References
- The Plant List, Carduus occidentalis Nutt.
- Calflora taxon report, University of California, Cirsium occidentale (Nutt.) Jepson, Cobweb Thistle, western thistle
- C.Michael Hogan ed. 2010. Cirsium occidentale. Encyclopedia of Life
- Jepson Flora Project (ed.). "Cirsium occidentale". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
- Biota of North America Program 2014 county distribution map
- Flora of North America, Western thistle, Cirsium occidentale (Nuttall) Jepson
- The Xerces Society (2016), Gardening for Butterflies: How You Can Attract and Protect Beautiful, Beneficial Insects, Timber Press.
- Jepson Flora Project (ed.). "Cirsium occidentale var. californicum". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
- "Plants Profile for Cirsium occidentale candidissimum (snowy thistle)". plants.usda.gov. Retrieved 2019-02-18.
- Jepson Flora Project (ed.). "Cirsium occidentale var. candidissimum". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
- Jepson Flora Project (ed.). "Cirsium occidentale var. compactum". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
- Jepson Flora Project (ed.). "Cirsium occidentale var. coulteri". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
- Jepson Flora Project (ed.). "Cirsium occidentale var. lucianum". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
- Jepson Flora Project (ed.). "Cirsium occidentale var. occidentale". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
- "Plants Profile for Cirsium occidentale venustum (cobwebby thistle)". plants.usda.gov. Retrieved 2019-02-18.
- Jepson Flora Project (ed.). "Cirsium occidentale var. venustum". Jepson eFlora. The Jepson Herbarium, University of California, Berkeley.
External links
- Jepson Manual treatment — Cirsium occidentale
- Cirsium occidentale — Calphotos Photo gallery, University of California
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