1. Carduus crispus L. (curly thistle, welted thistle)

Pl. 250 d–f; Map 1038

Stems 40–200 cm long, brittle, usually cobwebby-hairy. Leaves and stem wings armed with relatively weak, slender, straw-colored spines. Basal leaves 15–30 cm long, lanceolate to oblanceolate or elliptic, the upper surface glabrous or cobwebby-hairy, the undersurface cobwebby- to felty-hairy. Stem leaves 3–12 cm long, lanceolate to narrowly oblong-elliptic, the lobes mostly relatively short, broadly triangular to broadly ovate, the upper surface glabrous or cobwebby-hairy, the undersurface cobwebby- to felty-hairy. Heads solitary or in small clusters, erect, 1.2–2.5 cm in diameter, sessile or the stalk relatively short and spiny-winged to the tip or nearly so, cobwebby- to felty-hairy. Involucral bracts 6–14 mm long (including the spiny tip), 1–2 mm wide, narrowly lanceolate, the outer and median ones loosely ascending to spreading, not bent or reflexed at the tip, gradually tapered to a short, slender, relatively weak, straw-colored or light brown, spiny tip, the surfaces cobwebby-hairy. Pappus 9–12 mm long, white. Corollas 12–15 mm long. 2n=16. June–September.

Introduced, known thus far from a single historical collection from St. Louis County (native of Europe, Asia, introduced sporadically in the northeastern U.S. and adjacent Canada west to North Dakota and Arkansas). Roadsides and presumably open, disturbed areas.