240 coMPosiT.E. (('OMiM)srrK kamily.) 



34. POLYMNIA, L. 



Heads ruiiiate, iiiaiiy-rioworcMi ; the ravs jiistillati-, in asiii^^lc row ; tlmse of 

 tlic ilisk tiiltular, 5-tu(jtlio(l, sterile. Scales of ihu iiivoliicri' in two rows ; tlie 

 outer leatV, sjireatliiig ; the iuucr smaller, inciiihranateous, clas](ing the olio- 

 voitl fertile aehuuiu. Jieeeptaele chaffy. J'apjjiis none. — Coarse i)ranching 

 perennial herbs, with uiigulai' or lohed leaves, and heads of yellow flowers in 

 corymhose panicles. 



1. P. Canadensis, L. A'i.scid-pul)escent; lowest leaves opposite, peti- 

 okd, jiiiinatilid ; ihu upper alternate, angled or lobed ; outer scales of the 

 involucre acuminate, hairy and viscid ; rays shorter than the involucre. — 

 Mountains of North Carolina. July - August. — Stem 2° -5'^ high. Heads 

 small. Kays pale yellow. 



2. P. Uvedalia, L. Stem smooth, or rough-puhesccnt ; leaves l)roadly 

 ovate, S-o-lulied, cuar.sely toothed, rough ahove, jnibescent beneath, abruptly 

 contracted iuto a siuuate-winged ])etiole ; outer scales of the involucre ciliate, 

 obtuse; rays much longer than the involucre. — Rich soil. July -August. — 

 Stem 3° -6° high. Kays bright yellow. 



35. ACANTHOSPERMUM, Schrank. 

 Heads moncecious, railiate, many-flowered ; the rays pi.stillate, in a single 

 row; disk flowers starainate, tubular, .5-toothed. Involucre of 5 elliptical 

 scales. Keceptacle flat. Acheuia compressed, armed on the back with rigid 

 hooked prickles, and enclosed in the outer scales of the chaffy receptacle. — 

 Diffusely branching herbs, with opposite leaves, and solitary heads of yellow 

 flowers. 



1. A. xanthioides, DC. Prostrate, pubescent ; leaves petioled, oval or 

 obovate, toothed or entire; chaff of the receptacle which encloses the ache- 

 nium unarmed. — Introduced in wool from South America several years ago, 

 and now a widely dissemiuated pest. 



2. A. humile, DC, with the chaff of the receptacle armed with 2 spines, 

 occurs as a ballast weed at Pensacola. 



36. CHRYSOGONUM, L. 



Heads mnnv-flowered ; the rays 5, i)istillate. Disk flowers tubular, 5-toothed, 

 sterile. Scales of the involucre in 2 rows; the exterior oblong, leafy ; the 

 interior roundish, clasping the oval compressed 4-angled fertile achenia. 

 Receptacle flat, chaffy. Pappus a .slighlly lol)ed cup-shaped crown, divided 

 on tlie inside to the base. — A low hairy stoloniferous perennial herb, with 

 oval or spntulate-ol)long opposite crenate leaves, and single heads of yellow 

 flowers borne on a long peduncle. 



1. C. Virginianum, L. — Dry open woods, Florida to North Carolina. 

 Feb. -April. — Plant at first simple, producing from a tuft of radical leaves 

 a single peduncled head, afterward stoloniferous and branching. 



37. SILPHIUM, L. 



Heads manv-flowered : the rays numerous, pis'^illate, fertile, in a single 

 row. Disk flowers cylindrical, sterile; the style undivided. Scales of the 



