Compositaceae 419 
K. Outer involucre-bracts with spines nearly equalling the body. E. 
C. ochrocentrus Gr. (Yellow-spined Thistle) 
KK. Outer involucre-bracts with spines distinctly shorter than the body. 
L. Leaves canescent on both sides. 
M. Heads 3—4 cm. high. E. 
C. undulatus Nutt. 
MM. Heads 6—8 cm. high. E. (C. megacephalus.) 
C. undulatus megacephalus Gr. 
LL. Leaves green above. 
N. Leaves conspicuously prickly. E. 
C. breweri Gr. 
NN. Leaves with few prickles. E. 
C. palousensis Pip. 
BBB. All the involucre-bracts spine-tipped. W. E. 
C. lanceolatus L.- (Bull Thistle) 
CYNARIA L 
Plant 1—2 m. high (ours); growing about abandoned gardens. Leaves in ours 
pinnatifid, thinly white-woolly, 3—5 dm. long, mostly basal. Heads rayless, all alike, 
very large; involucre flat, wide, imbricated in several series, fleshy, often spine-tipped; 
receptacle bristly. Flowers white or blue or purple. Akenes beakless. Pappus plumose. 
(Gk. kyon—a dog; the involucre-spines suggest dog-teeth.) W. 
C. scolymus L. (Artichoke) 
SILYBUM MILK THISTLE 
Annual or biennial, ours 6—12 dm. high. Leaves clasping, sinuate-lobed to 
pinnatifid, white-blotched, prickly. Heads rayless; involucre depressed-globose; its bracts 
prickly at margin, with spreading spine at tip, in many series; receptacle densely bristly. 
Flowers perfect, purplish, deeply 5-cleft. Filaments united below, glabrous. Akenes 
oblong-obovate, flattish, glabrous, with a papillose ring at tip. Pappus-bristles in 2 or 
more whorls, barbellate (ours), white. (Gk. silybos—the name of a thistle with edible 
stem. ) W. E. S. marianum Gaert. (Lady’s Thistle) 
CENTAUREA STAR THISTLE 
Annual or perennial. Heads many-flowered; flowers all tubular but the the mar- 
ginal ones often much larger and sterile; involucre ovoid or globose, the bracts margined 
or appendages; receptacle bristly. Marginal flowers sometimes suggesting rays, color 
various. Akenes obovoid or oblong, flattish or 4-angled, with ring at tip, oblique at- 
tached. Pappus none or of bristles or of scales. (It is said that the centaur Chiron 
cured his wounded foot with these.) 
A.  Involucre-bracts spine-tipped. 
B. Stem not winged; corollas purplish; pappus none. W. 
C. calcitrapa L. (Caltrops) 
BB. Stem winged; corollos yellow; pappus of unequal bristles or scales. W. 
C. meltensis L. (Tocalote) 
AA. Involucre-bracts not spine-tipped. 
C. Annual; pappus of unequal bristles; corollas white or red or blue or violet. E. 
C. cyanus L. (Blue-bottle) 
CC. Perennial; pappus none; corollas red. E. 
C. consimilis Bor. 
