Cirsium occidentale (Nutt.) Jepson var. californicum (A. Gray)
Keil & C. Turner


California Thistle
Asteraceae (Sunflower Family)



 

California thistle is a slender, erect biennial herb with a branching, white-tomentose stem that can reach 6'-8' tall and becomes glabrate in age.  It is leafy near the base and almost bare above.  The leaves are alternate, sinuately to deeply pinnatifid, and moderately spinose.  They are also wavy-margined, green to gray above and gray below, and 4" to 14" long.  The discoid flowering heads are solitary on long slender peduncles, the involucres hemispheric and lightly cobwebby, about 1" high, with outer spreading phyllaries that have spiny tips and inner ones that are more erect and herbaceous.  There are disk flowers only which well exceed the involucres and pappi of white plumose bristles. Differentiating between Cirsium occidentale var. californicum (formerly C. californicum) and C. occidentale var. occidentale can be a bit difficult.  The stems of the former are generally more slender, the peduncles less than 1/8" in diameter, while those of the latter are between 1/8" and 3/16". Var. occidentale also has darker red to purple corollas that typically don't exceed the involucre, and much more densely cobwebby involucres.  Compare with the photo below. This species of thistle grows in disturbed places and on dry slopes and fans below 7000' in coastal sage scrub, chaparral and southern oak woodland, mostly away from the immediate coast, where the other variety is more common. California thistle blooms from April to July.

Click here for Latin name derivations: 1) Cirsium 2) occidentale 3) californicum.
Pronunciation: SIR-see-um ok-si-den-TAY-lee ka-li-FOR-ni-cum.
Click here for Botanical Term Meanings.

 




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