COMPOSITAE. 



243 



Pappus of capillary bristles. 

 Involucral bracts in one 



row. 

 Involucral bracts in several 

 rows. 

 Pappus a short crown or none. 

 Heads large, 1.5-2 cm. in 



diameter. 

 Heads small, 5 mm. or less 

 in diameter. 

 Lower leaves opposite. 

 Lower leaves alternate. 

 Leaves entire or 

 nearly so, ovate. 

 Leaves incised, or 

 if entire, lanceo- 

 late or linear. 

 Staminate and pistillate flowers in 

 different heads. 

 Pappus capillary; fertile invo- 

 lucre not bur-like. 

 Leaves prickly; heads large. 

 Leaves not prickly; heads 

 small. 

 Pappus of staminate 

 flowers either club- 

 shaped or barbed at the 

 apex. 

 Pappus of all the flowers 

 alike and neither club- 

 shaped nor barbed. 

 Pappus none; fertile involucre 

 bur-like. 

 Bracts of staminate heads sep- 

 arate; bur large, with many 

 scales. 

 Bracts of staminate heads 

 united; bur small, with 

 1-4 scales. 

 Spines in 1 row; pistillate 



flowers 1 in a head. 

 Spines in several rows; 

 pistillate flowers 1^1 in 

 each head. 

 Flowers of the heads all perfect and alike. 

 Pappus of separate capillary bristles. 

 Flowers whitish. 

 Flowers yellow or brownish. 



Involucral bracts in 3-4 rows. 

 Heads 2-3 mm. in dia- 

 meter. 

 Heads 20-30 mm. in di- 

 ameter. 

 Involucral bracts in 1 row or 

 nearly so. 

 Involucre campanulate. 

 Involucre hemispheric to 

 rotate. 



375. Petasites, 252. 



376. Gnaphalium, 252. 



374. Centaurea, 251. 



377. Iva, 253. 



378. Adenocaulon, 253. 



379. Artemisia, 253. 



387. Cirsium, 259. 



380. 



381. 



Antennaria, 254. 

 Anaphalis, 256. 



382. Xanthium, 256. 



383. Ambrosia, 257. 



384. Gaertneria, 258. 



385. Coleosanthus, 258. 



386. Chrysothamnus, 259. 



407. Hoorebekia, 273. 



408. Senecio, 274. 

 401. Erigeron, 266. 



