thistle, popular name for many spiny and usually weedy plants, but especially applied to members of the family Asteraceae (aster family) that have spiny leaves and often showy heads of purple, rose, white, or yellow flowers followed by thistledown seeds (a favorite food of the goldfinch). The Scotch thistle (variously identified, but most often as Onopordum acanthium, now cultivated as an ornamental) is the badge of the Scottish Order of the Thistle and the national emblem of Scotland. The blessed thistle, or St.-Benedict's-thistle (Cnicus benedictus, the Carduus benedictus of Shakespeare's Much Ado about Nothing, iii:4) was at one time a heal-all and is still sometimes used medicinally. The common, or bull, thistle (Cirsium lanceolatum) and the pasture thistle (Cirsium odoratum) are attractive weeds not to be confused with the so-called Canada thistle (Cirsium arvense), naturalized from Europe. A few thistles are cultivated in gardens, e.g., the large-flowered globe thistles, species of the Old World genus Echinops. The Russian thistle is a tumbleweed. Thistle is classified in the division Magnoliophyta, class Magnoliopsida, order Asterales, family Asteraceae.

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