The common name of cirsium occidentale
, cobwebby thistle, refers to the spherical cluster of long, sharply-spined phyllaries below the flowers, as these grow through a ball of a dense, cobweb-like material, which becomes more pronounced as the seeds form. The flower head is composed of hundreds of very narrow disc florets, each about 1.5 inches long, usually purple but sometimes red or whitish. Like the leaves, the thick, strong stems appear grey or even white due to a covering of hairs; the stem may reach a height of 10 feet or more, and branch quite profusely. Several varieties of this species are recognized, reflecting different characteristics of the corollas, involucres and growth habit.