174 DICOTYLEDONOUS PLANTS. 



t 



0. acantkium Linn. : leaves ovate-oblong, sinuate and spinous, de- 

 current, woolly on both sides ; scales of the involucre subulate, spread- 

 ing. 



HAB. Waste grounds. N. S. July. $ . Stem 4 6 feet high. 

 branched and winged to the summit ; wings very spinous. In- 

 volucre globose. Flmcers large, solitary, purple. Introduced. 



Cotton Thistle. 



13. CENTAUREA. Linn. 



Involucre scaly. Receptacle bristly. Carol of the ray in- 

 fundibuliform, irregular, larger than those of the disk, rap- 

 pus simple. Syngenesia. Frustratiea. 



1. C. jacea Linn. : leaves linear-lanceolate, the lower ones broader 

 and toothed ; scales of the involucre scariose and torn, the lower one* 

 pinnatifid. 



HAB. Penn. Muhl. July, Aug. If. Scales of the inrolurrc 

 pale-brown and shining, the outer ones deeply pinnatifid, the in- 

 ner or uppermost ones torn. Flowers purple. Introduced. 



Brown Knapweed. 



2. C. nigra Linn. : lower leaves angular-lyrate, upper ones ovate ; 

 scales of the involucre ovate, ciliated with capillary teeth. 



HAB. Mass, and Penn. July, Aug. U-St*m 23 feet high. 

 Leaves scabrous. Scales of the involucre almost black, the teeth 

 brown. Flowers solitary, terminal, purple. Introduced. Be- 

 sides the above, C. cyanus, C. benedicticta and C. calcitrapa are 

 naturalized in some parts of the United States. None of them 

 are indigenous. Black Knapicc&l. 



14. ELEPHANTOPUS. Linn. 



Partial involucre 4-flowered. Florets ligulate, 5-cleft, per- 

 fect. Receptacle naked. Pappus setaceous. 



Syngenesia. Segregata. 



E. carolinianvs Wittd. : stem branched, leafy, hairy ; leaves of the 

 root and stem oblong, tapering at base, hairy. 



HAB. Dry soils. Md. to Car. Sept. 2j..Stcm 2 feet high, 

 villous, especially near the base, branching towards the summit. 

 Heads of flowers composed of four clusters, each 4-flowered, 

 with the involucre 9 10-leaved. Corol purple. 



Elepfiant' s-foot. 



15. VERNONIA. Linn. 



Involucre ovate, imbricate. Receptacle naked. Stigma 

 bifid. Pappus double ; outer short, chaffy ; inner capillary. 



Syngenesia. JEqualis. 



