3. Sonchus oleraceus L. (common sow thistle)

Pl. 262 c, d; Map 1098

Plants annual, taprooted. Stems 10–200 cm long, glabrous or with sparse, spreading, reddish brown, gland-tipped hairs toward the tip, usually somewhat glaucous. Leaves with the clasping basal lobes mostly sharply pointed (less commonly some of them rounded), the margins with the teeth having relatively soft, short, slender prickles at the tips, glabrous, the upper surface somewhat darker green but not shiny, the undersurface pale and usually glaucous. Basal and lower stem leaves 4–40 cm long, usually irregularly and deeply lobed. Median and upper stem leaves gradually reduced in size, variously unlobed to more commonly shallowly or deeply lobed. Inflorescence branches usually sparsely pubescent with spreading, reddish brown, gland-tipped hairs, sometimes with minute, branched, cobwebby to woolly hairs toward the tip. Flowering heads 1.5–2.7 cm in diameter (measured across the spreading corollas). Involucre 9–13(–15) mm long, usually with at least a few spreading, reddish brown, gland-tipped hairs, sometimes also with minute, branched, cobwebby to woolly hairs toward the base when young. Corollas 8–15 mm long, light yellow to lemon yellow. Pappus 5–8 mm long. Fruits 2.5–3.0 mm long, faintly to noticeably 3- or 5-nerved on each face, also finely to relatively coarsely cross-wrinkled, yellowish brown to reddish brown. 2n=32, 36. June–October.

Introduced, scattered nearly throughout the state (native of Europe, introduced widely in North America). Pastures, banks of ditches, gardens, barnyards, railroads, roadsides, and moist, disturbed areas.

Steyermark (1963) noted that this species has been undercollected in Missouri, and it remains so today. The distribution map thus grossly underrepresents its actual distribution in the state.