38 



CI( HORIACEAE 



Vol. Ill 



Leaves glabrous. 



Leaves entire to pinnatifid, not sagittate at base. 

 Leaves entire or denticulate, sagittate at base. 



6. /.. canadensis. 



7. L. sagittifolia. 



B. Achenes truncate, or narrowed into stout beaks; rays blue to white. 



Perennial ; achenes flattened. 

 Annuals or biennials ; achenes swollen. 

 Pappus bright white. 



Achenes beakless; leaves dentate, acuminate. 

 Achenes beaked ; leaves pinnatifid. 

 Pappus brown ; achenes short-beaked. 



8. L.pulchella. 



9. L. villosa. 



10. L. ftoridana. 



11. L. spicata. 



races, differing in 



i. Lactuca virosa L. Prickly or \yild 

 Lettuce. Fig. 4068. 



Lactuca virosa L. Sp. PI. 795. 1753. 

 Lactuca Serriola L. Cent. PI. 2: 29. 1756. 

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



Biennial, green and glaucous ; stem stiff, leafy, 

 usually paniculately branched, glabrous through- 

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

 Leaves oblong or oblong-lanceolate, spinulose- 

 margined, denticulate or pinnatifid, sessile or 

 auriculate-clasping, the lowest sometimes 10' 

 long and 3' wide, the upper much smaller; 

 midrib spinulose or hispid; heads 2"-4" broad. 

 6-12-flowered ; very numerous in an open pan- 

 icle ; involucre cylindric, l"-lj" 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, Vermont to Georgia. 



west to the Pacific Coast. A troublesome weed. 



Naturalized from Europe. Consists of several 



the form, lobing and position of the leaves. Aug.-Sept. 



Milk- or horse-thistle. 



2. Lactuca saligna L. Willow Let- 

 tuce. Fig. 4069. 



Lactuca saligna L. Sp. PI. 796- J753- 



Biennial, light green ; stem slender, smooth 

 or nearly so, 2 high or more, the very 

 slender branches erect-ascending. Leaves 

 glabrous, linear to oblong, 6' long or less, 

 runcinate-pinnatifid with pointed divergent 

 lobes, or entire, sagittate at the base, the 

 midvein sometimes spinulose; panicles nar- 

 row ; heads about 3" broad, few-flowered ; 

 involucre subcylindric ; outer bracts much 

 shorter than the inner; achenes oblong, 

 about one-half as long as the filiform beak; 

 pappus white. 



Waste and cultivated grounds, Ohio. 

 uralized from Europe. July-Aug. 



Nat- 



