MOKOPETALOUS EXOGEl^OUS PLANTS. 351 



and entire; exterior scales of the involucre linear-spatulate; 

 acUenia smoothish, witli two short triangular teeth. (0. 

 mitis, Michx. ; C. arguta, Pursh.) Stem 2°-4° high; 

 leaves polymorphous, the uppermost commonly undivided; 

 rays showy. 



^;\ Leaves petiokd ; achenia elliptical or ob&vate^ emarginate, awiUess ; exterior 

 scales of the involucre shorter than the interior. 



C. TRiPTERis, L. Stem smooth, branching ; leaves smooth, 

 or rough above, the upper and lower ones entire, the middle 

 ones 3- (rarely 5) -parted, with the divisions lanceolate and 

 entire; exterior scales of the involucre 5-G, obtuse, united 

 at the base; achenia elliptical, smooth, incurved, narrowly 

 winged. Stem 3°-6° high. 



t+* Leaves sessile, Z-2)arted to the base, seemingly ^ina whorl, the divisions entire or 

 variousbj divided ; scales of the involucre equal, the exterior ones linear-oblong, 

 united below; achenia oblong, narrowly winged, naked or minutely 2-toothed 

 at the apex. 



C. VEHTiciLLATA, L. Smooth ; stem branching, slender ; 

 divisions of the pinnately or bipinnately divided leaves 

 linear or filiform ; disic yellow ; achenia minutely 2-toothed 

 at the apex. Stem l°-3° high. 



+t Says yeUow ; achenia nearly straight, obloJig, 2-awned, the margins with a serru- 

 late or pectinate toi7\g y exterior scales of the involucre shorter than the interior ; 

 disk dark purple. 



C. ANGUSTTFOLIA, Ait. Stem 2°-3° high, slender, 4-an- 

 gled, branched, smooth ; leaves linear, alternate or opposite, 

 obtuse, entire, the lower ones spatulate-lanceolate; heads 

 corymbose; rays 3-toothed, J' long; achenia-Vtrngs pecti- 

 nately toothed. 



t+t Rays purple or rose-color. 



C. ROSEA, Nutt. Smooth; stem low, branching; leaves 

 opposite, linear; heads small; rays slightly 3-toothed; 

 achenia wingless, unawned. Stem 8-12' high ; rays rose- 

 color. 



