1. Arctium minus (Hill) Bernh. (common burdock)
Pl. 250 a–c; Map
1037
Plants coarse, biennial,
with stout taproots. Stems 50–180 cm long, erect or ascending, usually
branched, stout, longitudinally ridged, not winged, minutely hairy, at least
toward the tip, often reddish- or purplish-tinged. Leaves basal and alternate,
long-petiolate (petioles of the basal leaves usually hollow), not decurrent,
the blades with the margins irregularly wavy or shallowly lobed and often also
toothed, the upper surface glabrous or with scattered hairs along the main
veins, the undersurface pale-colored, sparsely to moderately pubescent with
minute, few-branched hairs (these sometimes appearing cobwebby), sometimes
becoming nearly glabrous with age. Basal leaves with the blades 30–60 cm long,
narrowly to broadly ovate, more or less cordate at the base, rounded to bluntly
or sharply pointed at the tip. Stem leaves progressively smaller toward the
tip, ovate to triangular-ovate, shallowly cordate, truncate, or abruptly
tapered at the base, rounded to bluntly or sharply pointed at the tip,
sometimes abruptly tapered to a short, sharp point. Inflorescences axillary and
terminal, the heads sessile or short-stalked, appearing clustered or more
commonly in short, dense racemes. Heads discoid, the involucre broadly ovoid to
nearly spherical (sometimes appearing bell-shaped when pressed), 1.2–2.5 cm in
diameter, the florets all appearing similar and perfect. Receptacle flat, with
numerous bristles. Involucral bracts 4–13 mm long, the body narrowly
lanceolate, appressed-ascending, glabrous or somewhat glandular, occasionally
cobwebby-hairy, tapered to a long, stiff, ascending bristle, this hooked at the
tip (the innermost bracts often with somewhat flattened, hookless bristles).
Pappus of several unequal series of short, flattened, bristlelike awns, these 1–3
mm long, with short, ascending barbs, mostly shed individually by fruiting.
Corollas 7–9 mm long, pink to purple, often somewhat glandular. Fruits
appearing basally attached, 4–6 mm long, oblong or slightly narrower at the
symmetrical base, somewhat flattened, the surface finely wrinkled, grayish
brown with darker mottling. 2n=32, 36. July–October.
Introduced,
scattered sporadically nearly throughout the state (native of Europe, Asia,
introduced widely in North America). Rarely disturbed openings of mesic upland
forests and banks of streams; more commonly barnyards, feedlots, old fields,
pastures, railroads, and open, disturbed areas.
Young stems of
burdock are eaten fresh or more commonly baked or boiled. The young herbage
sometimes also is eaten by livestock. The thick roots can be cooked and eaten,
and in the past they sometimes were dried and ground for use as a filler in
coffee. They also have been used medicinally as a laxative, diuretic, to lessen
the symptoms of rheumatism, and in a paste to treat burns and sores
(Steyermark, 1963). The burlike heads are dispersed mostly in animal fur, and
the individual fruits are shed from the head very tardily.
Most plants have
pink to light reddish purple corollas. Rare individuals with darker purple
corollas have been called f. purpureum (Blytt) A.H. Evans, and
white-flowered plants are known as f. pallidum Farw.
Steyermark
(1963) treated A. tomentosum Mill. (cotton burdock) based on historical
collections from Jackson
County. However,
Mühlenbach (1983) concluded that all of these specimens were misdetermined
plants of A. minus. Arctium tomentosum is another Eurasian species that
is weedy in the New World. It differs from A.
minus in its shorter, more flat-topped inflorescences with mostly
long-stalked, generally slightly larger heads, and corollas that are usually
somewhat glandular on the outer surface (Moore and Frankton, 1974). The few Missouri specimens in
question do have longer stalks, but the heads otherwise resemble those of A.
minus, and the inflorescences overall are elongate rather than flat-topped.