426 Compositaceae 
A. Involucre glandular-pubescent, 25 mm. high; flowers bright-yellow; perennial; 
leaves with acute basal angles; akenes transversely wrinkled. W. E. 
S. arvensis L. (Field Sow-thistle) 
AA. Involucre glabrous, 12—16 mm. high; flowers pale-yellow; annual. 
B. Leaves with acute basal angles; akenes transversely wrinkled. W. 
S. oleraceus L. (Common Sow-thistle) 
BB. Leaves with rounded basal angles; akenes not transversely wrinkled. W. E. 
S. asper Hill (Prickly Sow-thistle) 
LACTUCA LETTUCE 
Stems tall, leafy. Heads in panicles, small; involucre-bracts imbricated in several 
series, the outer shorter; receptacle naked. Corolla yellow or blue or purple. Akenes 
oval or oblong or linear, flat, 3—5-ribbed on each face, narrowed above or contracted 
into a narrow beak; beaks sometimes expanded disk-like under pappus. Pappus of bris- 
tles; bristles capillary, soft, many, white or brown. (L. lac—milk; from the abundant 
milky juice. ) 
A. _Pappus brownish; flowers blue; plant |—3.5 m. high; involucre 1012 mm. long; 
leaves not prickly on the mid-veined beneath. W. C. E. 
L. .spicata Hitch. 
AA. Pappus white; flowers rarely blue, mostly yellow. 
B. Leaves not prickly on the mid-veins beneath. 
C. Flowers blue; perennial; involucre 16——20 mm. long; akene and its beak 
about 1/3 as long as the pappus. W. E. 
16, pulchella DC. . (Blue Lettuce) 
CC. Flowers yellow, rarely purplish; annual or biennial; involucre 8—14 mm. 
long; akene and its beak about as long as the pappus. 
D. Heads 12—20-flowered; akenes |-veined on each face. W. 
L. sativa L. (Garden Lettuce) Z 
DD. Heads 6—12-flowered; akenes several-veined on each face; plant |—4 
m. high. 
E. Leaves strictly entire. E. 
L. sagittifolia Ell. 
EE. Leaves except the upper ones sinuate-pinnatifid. E. 
L. canadensis L. (Wild Lettuce) 
BB. Leaves prickly on the mid-veins beneath; flowers yellow; akene about equaling 
its beak. 
F. Leaves oblong-lanceolate, sinuate-pinnatiid. W. E. 
L. scariola L. (Prickly Lettuce) 
FF. Leaves oblanceolate, merely irregularly denticulate. W. E. 
L. scariola integrata G. & G. 
LYGODESMIA 
Perennial (ours), smooth; stems rigid or rusk-like; some of the branches some- 
times reduced to spines. Leaves lanceolate or linear, or scale-like by reduction. Heads 
scattered or terminating the branches, 3—12-flowered; principal involucre-bracts 5—8, 
linear, scarious-margined, equal, with several very short ones outside; receptacle naked. 
Corolla pink or rose-colored. Akene terete, obscurely ribbed or veined, usually linear or 
slender-fusiform, sometimes attenuate but hardly beaked. Pappus of bristles; bristles 
soft or somewhat rigid, capillary simple, white to brownish, usually- somewhat unequal. 
(Gk. lygos—a twig, desma—=a bundle; referring to the tufted rush-like stems. ) 
