1316 CICHOEIACEAE 



6. LACTUCA L. 



Annual, biennial or perennial often coarse herbs, with glabrous or sometimes prickly 

 foliage. Stems often tall, racemose or paniculate above. Heads white, yellow or 

 blue, rather small, often numerous. Involucres cylindric: bracts disposed in 2 

 involucres, the inner of 1 or 2 series of nearly equal bracts, the outer of several series 

 of much shorter bracts, or the outer and inner bracts gradually merging. Keceptacle 

 flat, naked. Ligules often inconspicuous, truncate and toothed at the apex. Anthers 

 sagittate at the base. Stigmas usually slender. Achenes flattened, oval to linear, 

 3-5-ribbed, narrowed above, sometimes into a neck, sometimes into a slender beak. 

 Pappus copious, of hair-like white or brown bristles. LETTUCE. WOOD LETTUCE. 

 WILD LETTUCE. 



Pappus bright white. 



Leaf-blades spiny-toothed and often spiny along the midrib beneath: corollas yellow. 

 Involucres 6 12-flowered. 1. L. virosa 



Involucres 12-20-flowered. 



Involucres over 1.5 cm. high: beak fully as long as the body of the 



achene. 2. L. Ludoviciana, 



Involucres less than 1.5 cm. high: beak shorter than the body of the 



achene. 3. L. sagittifolia. 



Leaf-blades without spines on the margins or midribs. 

 Achenes thin, each prolonged into a slender beak. 



Involucre of 2 sets of bracts; outer very short; inner much longer: 



corollas yellow to reddish, except sometimes in No. 6. 

 Leaf-blades, at least some of them, pinnatifid. 



Leaves glabrous. 4. L. Canadensis. 



Leaves hirsute, at least their midribs. 



Lower leaf-blades all pinnatifid : beak of achene fully as long 



as the body. 5. L. hirsuta. 



Lower leaf-blades usually both entire and pinnatifid: 



beak of achene much shorter than the body. 6. L. graminifolia. 



Leaf-blades entire or merely toothed. 3. L. sagittifolia. 



Involucre with the outer and inner bracts connected by intermediate 



series: corollas blue. 7. L. pulchella. 



Achenes thick, beakless, sometimes contracted into a neck. 



Leaf-blades toothed: achene-body not narrowed into a neck. 8. L. villosa. 



Leaf-blades pinnatifid: achene-body narrowed into a slender neck. 9. L. Floridana. 

 Pappus brown. 10. L. spicata. 



1. Lactuca virosa L. Biennial, bright green, glaucous. Stems erect, 6-20 dm. 

 tall, rigid, glabrous at least above the more or less hirsute base, paniculate above: 

 leaves numerous; blades oblong to oblong-lanceolate, or oblanceolate, 1-3 dm. long or 

 shorter above, denticulate, and spinulose beneath, sessile and clasping: heads 6-12- 

 flowered, 4-8 mm. broad: involucre 10-13 mm. high; inner bracts longer than the 

 outer, narrowly linear, green : ligules yellow : achenes ribbed, thick-margined, the body 

 fully 3 mm. long, sometimes surpassed in length by the slender beak. 



In waste places, fields and thickets ; New York to Kansas, south to Georgia and Ten- 

 nessee. Summer and fall. 



2. Lactuca Ludoviciana (Nutt.) DC. Biennial, glabrous. Stems erect, 4-15 

 dm. tall, paniculately branched above: leaves numerous; blades oblong-oblanceolate to 

 oblong or oblong-lanceolate, 5-20 cm. long, acute or short-acuminate, sinuate-lobed or 

 pinnatifid, spinulose along the margins as well as the midnerve beneath, clasping: 

 peduncles with few scales: heads in close or open panicles: involucres 16^20' mm. high; 

 inner bracts linear-lanceolate, scarious-margined : ligules yellow: achenes brown or 

 black, the body obovate or oval, 4 mm. long, 3-ribbed, the beak fully as long as the 

 body. 



On plains and prairies, Minnesota to North Dakota, Arkansas and Texas. Summer 

 and fall. 



3. Lactuca sagittifolia Ell. Biennial, glabrous. Stems erect, 1-3 m. tall, panic- 

 ulate above: leaf -blades spatulate, oblanceolate to oblong-elliptic, or lanceolate, 1-3 

 dm. long, acute or somewhat acuminate, irregularly dentate, narrowed at the base but 

 sessile and partly clasping: peduncles more or less scaly: involucres 10-20 mm. high; 

 inner bracts linear to linear-lanceolate: ligules yellow or reddish: achenes 5 mm. long, 

 not wing-margined, strongly ribbed, the body longer than the beak. 



On banks and in dry soil, New Brunswick to Ontario, Nebraska and Georgia. Summer 

 and fall. 



4. Lactuca Canad6nsis L. Biennial, glabrous. Stems erect, 1-3 m. tall, panicu- 

 late above, often mottled: leaf -blades various, those of basal-leaves spatulate or 



