MONOPETALOUS EXOGENOUS PLANTS. 363 



N. viKGATUS, DC. Stem 2°-4°, smooth, virgate, sim- 

 ple ; leaves lanceolate, acute, sessile, amplexicaul ; upper 

 leaves small, entire, the lowest pinnatifid on margined pe- 

 tioles ; heads small clusters, racemed ; involucre smooth, 

 purplish, of 8 scales, 8-12-flowered ; pappus straw-colored ; 

 floioers purplish. 



LYGODESMIA, Don. 



Heads solitary, 5-10-flowered ; leaves linear or filiform ; 

 receptacle naked ; achenia linear, elongated, smooth, 

 striate, not narrowed upward; pappus of copious hairs, 

 white, in several rows ; /ozf^ers rose-color. — Perennial herls, 



L. APHYLLA, DC. Stem l°-2°, simple or forking; leaves 

 filiform, elongated, on the lower part of the stem ; the 

 upper are remote, small, and bract-like ; heads showy. 



PYRRHOPAPPUS, DC. 



Heads many-flowered; involucre double, of numerous 

 subulate scales, the inner ones ei'ect and partially united, 

 often with a callous appendage at the apex ; receptacle flat, 

 naked ; achenia oblong, nearly terete, Sfurrowed, the apex 

 narrowed into a long filiform beak ; pappus of copious soft 

 reddish or brownish hairs. — Smooth annual herbs ; leaves 

 oblong or lanceolate, commonly toothed or pinnatifid ; heads 

 solitary, terminating the naked stem or peduncle-like 

 branches ; floioers yellow. 



P. Carolinianus, DC. Stem branching ; leaves lanceo- 

 late, mostly toothed or pinnatifid ; achenia shorter than 

 the filiform beak. Stem l°-2° high. 



LACTUCA, L. Lettuce. 



Heads few or many-flowered ; scales of the cylindrical 

 involucre imbricated, the outer ones short; receptacle 

 naked ; achenia compressed parallel to the scales, smooth. 



