AMBROSIACEAE 1149 



Leaf-blades much longer than broad : leaf-bases accompanied by 3-pronged spines. 



1. X. spinosum. 

 Leaf-blades as broad as long or but little longer : leaf-bases without spines. 



Fruit glabrous or nearly so, the beaks nearly straight. 2. X. glabratum. 



Fruit pubescent, the beaks incurved or hooked. 

 Fruit less than 2. .5 cm. long. 



Body of fruit oblong, twice as long as thick. 3. X. Pennsylvanicum. 



Body of fruit oval, less than twice as long as thick. 4. X echinntum. 



Fruit over 2.5 cm. long. 5. X speciosum. 



1. Xanthium spinosum L. Bright green, armed with yellow 3-forked spines. 

 Stems erect, 2-10 dm. tall, usually much branched : leaf-blades thickish, lanceolate, 

 entire or 3-lobed, the lobes acute or acuminate, minutely pale- or white-pubescent beneath : 

 staminate involucres many-flowered ; bi-acts narrow : corolla 2-2.3 mm. long ; lobes tri- 

 angular : pistillate involucres solitary or few together : fruit oblong-cylindric, 10-13 mm. 

 long, hard, pubescent, armed with hooked prickles and terminating in subulate beaks. 



In waste places or on river banks, Ontario to Missouri, Florida and Texas. 



2. Xanthium glabratum (DC.) Britton. Glabrate, or finely pubescent, unarmed. 

 Stems erect, 2-13 dm. tall, usually branching : leaf-blades ovate or deltoid, 5-30 cm. long 

 and broad or smaller above, acute or acutish, rather coai^ely toothed and more or less dis- 

 tinctly lobed, truncate or cordate at the base ; petioles about as long as the blades or 

 shorter: fruit oblong, 1.5-2 cm. long, glabrous or merely puberulent, thickly beset with 

 slender, more or less strongly hooked spines, terminating in straight or nearly straight 

 beaks. 



In waste places, New England to Xebraska, Florida and Mexico. 



3. Xanthium Pennsylvanicum Wallr. Eough-pubescent, at least above. Stems 

 2-6 dm. tall, relatively slender : leaf-blades thin, glandular, sharply toothed or some of 

 them 3-5-lobed : fruit oblong, 1.5-1.8 cm. long, puberulent and resinous-glandular, and 

 commonly with scattered hairs, with incurved and hooked beaks, the prickles numerous, 

 nearly as long as the diameter of the fruit-body. 



On river banks or in rich soil, Ontario to Minnesota, District of Columbia and Arkansas. 



4. Xanthium echinatum Murr. Rough-pubescent. Stems erect, 3-16 dm. tall, 



usually branching, often spotted with brown : leaf-blades ovate, deltoid to reniform, acute, 



coarsely toothed and often shallowly lobed, truncate or cordate at the base ; petioles as 



long as the blades or shorter : fruit oval, 2-2.3 cm. long, hispid, thickly beset with stout, 



rigid more or less strongly hooked prickles, terminating in incurved or hooked beaks. 



On river banks, beaches and in waste places, the Great Lake region to Vermont, Massachusetts 

 and North Carolina. 



5. Xanthium speciosum Kearney. Somewhat pubescent. Stems erect, 1-1.5 mm. 

 tall, stout, much branched, 4-angled, zigzag above, rigid : leaf-blades thickish, dull-green, 

 broadly triangular-ovate, often broader than long, 15-22 cm. broad or smaller above, shal- 

 lowly 3-5-lobed, scabro-pubescent on botli sides, prominently nerved, especially beneath, 

 cordate : petioles rather slender, 10-15 cm. long or shorter above, pubescent especially 

 along the deep groove : fruit ovoid, 2.5-4 cm. long, with 2-3 stout more or less incurved 

 beaks, 10-12 mm. long, closely armed with more or less incised prickles, 8-9 mm. long, 

 pubescent and resinous-dotted. 



In sandy bottoms, North Dakota to Tennessee and Texas. 



2. GAERTNERIA Medic. 



Annual or perennial caulescent herbs, simulating species of Ambrosia, with variously 

 pubescent foliage. Leaves alternate or usually so : blades lobed or divided. Heads monoe- 

 cious : staminate in terminal spikes or racemes : pistillate solitary or clustered below the 

 staminate. Staminate involucre open, usually hemispheric, with the 5-12 bracts partially 

 united : receptacle chaffy : corolla short ; lobes 5 : anthers scarcely coherent : styles 

 simple. Pistillate involucres closed, globose to ovoid, with 1-4 cavities and beaks, and 

 spines in several rows, becoming bur-like at maturity : stigmas 2. Achenes broadest 

 above the middle, solitary in each cavity of the involucre. [Franseria Cav. ] 



1. Gaertneria tenuifolia (A. Gray) Kuntze. Perennial, herbaceous, the foliage 

 often hispid. Stems erect, 3-15 dm. tall, leafy to the inflorescence : leaves numerous, 5-15 

 cm. long ; blades 2-3-pinnately parted or even dissected into narrow segments : staminate 

 heads in slender usually panicled racemes : pistillate heads clustered, usually numerous, 

 involucre either 1- or 2-flowered : fruit fully 2 mm. long, with 6-18 short incurved spines. 



In moist grounds, Texas to Colorado, California and Mexico. Summer and fall. 



