$YNGENESIA NECESSARIA. Ambrosia: $81 
On the banks of ponds and ditches: Pensylvania and 
Virginia. - ©. July—Sept. v. v. The flowers of 
this genus are very inconspicuous, 
2. A. hirsutissima ; foliis arcte sessilibus simplicibus oblon- bidentata. 
gis supra basin latescentem utrinque unidentatis, fruc- 
tu tetragono infra apicem quadrispinoso. Mich. fi. 
amer. 2. p. 182. 
In the western parts of the Allegany mountains (9. 
July—Sept. v.v. | 
3. A. hirsuta, aspera ; foliis 3-lobis serratis, lobis ovali-lan- trifida. 
ceolatis acuminatis, fructu infra apicem O-spinoso.— 
Willd. sp. pl. 4. p. 375. 
Icon. Moris. hist. 3. s. 6. t. 1. f. 4. 
On the banks of rivers and ditches: Pensylvania to Ca- 
rolina. ©. Aug. Sept. v. v. From. five to eight 
feet high. 
4, A. foliis bipinnatifidis glabriusculis, petiolis longe cilia. - elatior. 
tis, racemis terminalibus paniculatis, caule virgato. 
Willd. sp. pl. 4. p. 376. 
In old fields: Canada to Carolina. ©. June—Aug. v.v. 
5. A. foliis bipinnatifidis subtus canescentibus summis pin- artemisifolia. 
nutifci, racemis terris terminalibus, ramis fastigiatis, 
Willd. sp. pl. 4. p. 376. 
fü fields and waste grounds: Pensylvania to Carolina. 
©. Aug. Sept. v.v. 
6. A. foliis glabris bipinnatifidis summis pinnatifidis, race- paniculata. 
mis terminalibus solitariis, ramis fastigiatis. Willd. sp. 
fl. 4. p. 376. 
Icon. Pluk. alm. t. 10. f. 5. : 
In old fields and on road sides: Canada to Florida. ©. 
July—Sept. v.v. 
7. A. foliis caulinis pinnatifidis subdentatis petiolatis, rameis heterophylla. 
summis lanceolatis sessilibus, petiolis longe ciliatis, 
* racemis terminalibus solitariis, caule paniculato: 
W ilid. sp. pl. 4. p. 378. ; 
On the banks of rivers and ditches: near Philadelphia, 
©. July—Sept. v.v. 
667. XANTHIUM, Gen. pl. 1426. 
1. X. caule inermi ramoso, foliis cordatis lobatis serratis Strumarium. 
scabris basi trinervibus, fructibus ellipticis pubescenti- 
bus setis rigidis uncinatis.—-Willd. sp. pl. 4. p. 373. 
