MONOPETALOUS EXOGENOUS PLANTS. 345 



one elongated; fruit down}", unarmed. Sandy shores at 

 Key West, forming large clusters. 



A. ARTE.MISI.EFOLIA, L. Anuual, erect, hairy or smooth- 

 ish ; leaves bipiiinatifid, witli linear lobes, the upper often 

 entire; spikes single or panicled; fertile /o?6'c?-5 single, 

 clustered, or sometimes spiked; fruit nearly globose, armed 

 with six short teeth. Stem l°-4° high. 



XANTHIUM, Tourn. Cocklebur. 



Heads monoecious, spiked, tlie upper ones many-flowered, 

 sterile, with the scales of the involucre separate, in a single 

 row; the receptacle oblong, chaffy, and the short corolla 

 5-toothed; the lower ones fertile, consisting of two pistil- 

 late flowers, inclosed in a 2-celled oblong closed involucre, 

 which is armed externally with numerous hooked spines or 

 bristles, and terminated by one or two stout beaks; corolla 

 filiform; acheiiiuni oblong, solitary in each cell. — Coarse 

 annual herbs; leaves alternate, lobed and petioled. 



X. STRU.MARIU.M. Stem l°-4° high, spineless, rough, 

 branched; leaves broadly cordate, large, lobed, the lobes 

 tootheJ-acute, rough on both sides; fi'uit oval, pointed by 

 two straight and smooth beaks. 



ECLIPTA, L. 



Annuals, rough, branching; heads small, axillary-pe- 

 duncled; flowers white; recejjtacle flat, chaff bristly ; ache- 

 nia 3-4-angled, hairy at the apex; many-flowered, the 

 ray flowers short pistillate, in a single row; diskflozvers 

 tubular, 4-toothed, perfect; pappus none; scales of the 

 involucre 10-12 in two rows; white. 



E. ERECT A. Stem l°-2° high, erect or diffuse, terete, 

 tumid below the joints; leaves oblong-lanceolate, acute, 

 serrate, narrowed into a petiole, covered like the stems 

 with hairs ; peduncles 2-3 together. 



15* 



