1028 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



Key to the species 



1. Achenes strongly 3 (5-) -ribbed on each face, thin-margined, not transversely 

 wrinkled; auricles of the leaf base rounded 1. S. asper. 



1. Achenes striate and also strongly wrinkled transversely, not thin-margined; 

 auricles of the leaf base acute 2. S. oleraceus. 



1. Sonchus asper (L.) Hill, Herbarium Brit. 1: 47. 1769. 



Sonchus oleraceus var, asper L., Sp. PI. 794. 1753. 



Here and there in Apache, Yavapai, Maricopa, Pinal, Cochise, 

 and Pima Counties, 1,100 to 8,000 feet, roadsides and waste ground, 

 April to August. An abundant weed nearly throughout North 

 America; naturalized from Europe. 



2. Sonchus oleraceus L., Sp. PL 794. 1753. 



Maricopa, Pinal, and Pima Counties, roadsides and waste places, 

 April to September. An abundant weed in most parts of North 

 America; naturalized from Europe. 



A gum obtained by evaporation of the juice of this plant is said 

 to be a powerful cathartic, and it has been used as a so-called cure for 

 the opium habit. 



139. LACTUCA. Lettuce, wild lettuce 



Annual or perennial herbs, nearly or quite glabrous, leafy-stemmed; 

 leaves variable, from linear and entire to oblong and pinnatifid; 

 heads small or medium-sized, panicled, yellow or blue; involucre 

 rather slender, more or less strongly graduated; achenes strongly 

 flattened, abruptly or gradually beaked; pappus copious, of soft 

 white capillary bristles. 



The garden lettuce is L. sativa L. Lactucarium, a sedative, is 

 obtained from L. virosa. Sheep sometimes feed on L. pulchella, but 

 the plant is reputed to be slightly poisonous. 



Key to the species 



1. Achene lanceolate or lance-oblong, strongly several-ribbed on each face' 

 gradually narrowed into a short stoutish beak; flowers blue. 



1. L. PULCHELLA. 



1. Achene oval or oval-oblong, abruptly narrowed into a slender beak sometimes 



as long as the body; flowers yellow or purplish (2). 



2. Achene small, the body 3 mm. long or less, light gray, about 5-nerved on 



each side, finely hispidulous above, not rugulose, the beak very slender, 



longer than the achene; leaves stiffly spinulose on the margin and usually 



on the midrib beneath 2. L. serriola. 



2. Achene larger, the body 4 to 6 mm. long, dark brown or blackish, 1 -nerved 



on each side, not hispidulous, finely trans verse-rugulose ; leaves not 



stiffly spinulose (3) . 



3. Achene with a body about 6 mm. long, the beak about half as long; 



leaves mostly narrowly linear and entire, the lower ones often broader 



and pinnatifid 3. L. graminifolia. 



3. Achene with a body about 4 mm. long, the beak about as long; leaves 

 all obovate or oblong, at least the lower ones pinnatifid, the upper ones 

 often not lobed 4. L. ludoviciana. 



1. Lactuca pulchella (Pursh) DC, Prodr. 7: 134. 1838. 



Sonchus pulchellus Pursh, Fl. Amer. Sept. 502. 1814. 



Apache, Navajo, and Coconino Counties, 6,000 to 7,500 feet, 

 summer. Saskatchewan to British Columbia, south to Missouri, 

 New Mexico, Arizona, and California. 



