Vol. III.] 



CHICORY FAMILY. 



273 



15. LACTUCA L. Sp. PI. 795. 1753. 

 Tall leafy herbs, with small panicled heads of yellow white or blue flowers, and alter- 

 nate leaves. Involucre cylindric, its bracts imbricated in several series, the outer shorter, or 

 of I or 2 series of principal nearlj' equal inner bracts, and several rows of short outer ones. 

 Receptacle flat, naked. Rays truncate and 5-toothed at the summit. Anthers sagittate at 

 the base. Style-branches mostly slender. Achenes oval, oblong or linear, flat, 3-5-ribbed 

 on each face, narrowed above or contracted into a narrow beak, which is somewhat expanded 

 at the summit into a small disk bearing the copious soft capillary white or brown pappus- 

 bristles. [The Ancient Latin name, from /etc, milk, referring to the milky juice. ] 

 .\bout 95 species, natives of the northern Iieniisphere. 



vr Pappus bright white. 

 1. Leaves spiny-margined and often with spiny or hispid midribs; flowers yellow. 

 Heads 6-i2-flowered: involucre very narrow, 4"-6" high. i. L. Scariola. 



Heads 12-20-flowered: involucre broader. 



Involucre S"-q" high; achene about as long as its beak. 2. /,. Ludoviciana. 



Involucre 4"-6" high; achene longer tlian its beak. 5. L. sagittifolia. 



2. Leaves neither spiny-margined nor with spiny midribs. 

 I a) Achenes very thin, flat, contracted into filiform or tapering beaks. 

 •Outer involucral bracts abruptly shorter than the inner; heads 4"-y" high; flowers yellow. 

 Leaves, or some of them, pinnatifid. 



Plant glabrous throughout. 3°-io° high. 

 Leaves, at least their midribs, hirsute; plant i°-6° high. 

 Leaves entire or dentate, none of them pinnatifid. 



Leaves oblong or oblong-lanceolate; achene longer than tlie beak. 

 Leaves lanceolate; achene about equalling the beak. 

 Outer bracts gradually shorter; heads 8"-io" high; flowers blue. 



(b) Achenes beakless or with short necks, thickish; flo%vers blue. 

 Leaves oblong to ovate, acuminate, dentate. 7. L. villosa. 



Leaves pinnatifid, the terminal segment commonly triangular. 8. L. Floridana. 



-X- -X- Pappus brown; flowers blue. 9. jL. spicata. 



I. Lactuca Scariola L. Prickly 

 Lettuce. (Fig. 3537.) 



Lactuca Scariola L. Sp. PI. Ed. 2, 11 19. 1763. 



Biennial, green and glaucous; stem stiff, leafy, 

 usually paniculately branched, glabrous through- 

 out, or hirsute at the base, 2°-"° high. Leaves 

 oblong or oblong-lanceolate, spinulose-mar- 

 gined, denticulate or pinnatifid, sessile or auricu- 

 late-clasping, the lowest sometimes 10' long and 

 3' wide, the upper much smaller; midrib spinu- 

 lose or hispid; heads 2"-4" broad, 6-i2flowercd; 

 very numerous in an open panicle ; involucre cyl- 

 indric, \"-iyz" thick, its outer bracts about 

 one-third the length of the inner; rays yellow; 

 achenes obovate-oblong, about as long as the 

 filiform beak; pappus white. 



In fields and waste places. New York and Penn- 

 sylvania to Minnesota and Missouri. A trouble- 

 some weed. Naturalized from Europe. Aug-Sept. 



3. L. Canadensis. 



4. L. hirsuia, 



5. L. sagiilifolia. 

 3. /,. Canadensis. 



6. L. pulchella. 



2. Lactuca Ludoviciana (Nutt.) DC. 

 Western Lettuce. (Fig. 3538.) 



Sonchus /.udovicianus i^vM.. Gen. 2: 125. 1818. 

 I.acluca Ludoviciayia DC. Prodr. 7: 141. 183S. 



Biennial, glabrous throughout, leafy up to inflor- 

 escence, paniculately branched, 2°-5° high. Leaves 

 oblong to ovate-oblong, acute or acutish, 2'-4' long, 

 auriculate-clasping, spiuulose-denticulate, sinuate- 

 lobed, or pinnatifid with spinulose segments; heads 

 3"-5" broad, numerous in an open panicle, their 

 peduncles bracteolate; involucre cylindric or ovoid- 

 cyliudric, glabrous, ?>"-()" high, its bracts success- 

 ively shorter and broader, the lower ones ovate; 

 rays yellow; achenes oval to obovate, flat, about the 

 length of their filiform beak; pappus white. 



Plains and banks, Iowa. Minnesota and Dakota to 

 Kansas and Texas. July-Sept. 



18 



