1. Silybum marianum (L.) Gaertn. (milk thistle, blessed milk thistle)
Map 1060
Plants coarse,
annual or biennial, with taproots. Stems 60–180 cm tall, erect, usually
branched, not winged, finely cobwebby-hairy. Leaves basal and alternate, mostly
sharply pointed and spiny at the tip, spiny along the often somewhat corrugated
or wavy margins, usually thinly pubescent with cobwebby hairs when young,
glabrous at maturity, strongly white-mottled, particularly along the main
veins. Basal leaves in a dense, overwintering rosette, sessile or
short-petiolate, the blades 15–80 cm long, 5–40 cm wide, elliptic, pinnately
lobed, the lobes more or less triangular to hemispherical, irregularly and mostly
shallowly lobed. Stem leaves mostly sessile, the blades gradually reduced
toward the tip, 1–40 cm long, elliptic to narrowly ovate or the uppermost
lanceolate, irregularly toothed or shallowly pinnately lobed, the bases not
decurrent, those of all but the lowermost leaves clasping the stem.
Inflorescences terminal, the heads mostly long-stalked, solitary at the branch
tips, sometimes somewhat nodding. Heads discoid, the involucre 30–45 mm long,
broadly ovoid to hemispherical, the florets all appearing similar and perfect.
Receptacle flat or slightly convex, with numerous bristles. Involucral bracts
glabrous, 25–40 mm long, somewhat thickened and fleshy or leathery; all but the
uppermost with the body appressed, oblong-ovate to narrowly ovate, finely and
sharply toothed along the margins, the tip with a well-developed appendage,
this spreading, lanceolate, the upper surface concave, spiny along the margins,
tapered to a stout, straw-colored to light brown, spiny tip; uppermost bracts
with the body lanceolate, the appendage less strongly differentiated,
ascending, tapered to a sharply pointed or short-spined tips. Pappus of
numerous unequal capillary bristles, these 15–20 mm long, fused at the base,
roughened with minute, ascending barbs or teeth, white, shed as a unit before
fruiting. Corollas 28–35 mm long, reddish purple to purple. Stamens with the
filaments fused into a short tube toward the base. Fruits appearing basally or
slightly obliquely attached, 6–7 mm long, oblong-obovate in outline, somewhat
flattened, with a minute, raised crown at the tip, the surface glabrous, shiny,
dark brown to black, often with lighter streaks or mottling, the apical crown
yellow. 2n=34. May–July.
Introduced, known
only from historical specimens without further locality data and from the city
of St. Louis (native of Europe, Asia, introduced widely in North America).
Open, disturbed areas.
Steyermark
(1963) overlooked the few historical voucher specimens during his research on
the state’s flora and did not treat this species. The vernacular and scientific
names are derived from Christian folklore, in which the mottling of the leaves
was purported to have developed following exposure to a drop of the Virgin Mary’s
milk. Silybum marianum is sometimes grown as a garden ornamental,
although in some western states it has become a rangeland weed. The species has
a long history of use in Europe and Asia for its food and medicinal value. The
immature heads and young herbage can be cooked and eaten as vegetables, and
boiled plants were once consumed in the springtime as a blood cleanser (Moore
and Frankton, 1974). The fruits (kenguel seed) also were formerly a component
of some bird seed mixes and were ground as a substitute for coffee (Mabberley,
1997). The principal medicinal uses date back to the time of Dioscorides and
involve the use of a seed extract for treatment of poisoning and ailments of
the liver, including jaundice and hepatitis. Such treatment is still popular in
Europe, and milk thistle pills also are available commercially in the United
States as an herbal dietary supplement to maintain liver health. Studies have
shown milk thistle extract to contain flavonoids effective in the treatment of Amanita
Pers. (death angel mushrooms) poisoning (Mabberley, 1997).