23. Xanthium L. Cocklebur 



Taprooted annuals, 2-20 dm. tall; leaves alternate (those at the very lowest 

 nodes opposite), petiolate, often irregularly toothed or even lobed, several cm. 

 long; heads axillary, nearly sessile, unisexual; pistillate heads in the middle axils, 

 burlike, the involucre nearly obovoid and completely enclosing the 2 pistillate 

 flowers, forming a conspicuous 2-chambered bur, prickly on the outside; flowers 

 without any corolla or pappus, the achenes solitary in the chambers of the bur; 

 staminate heads in the upper axils much smaller; involucre cup-shaped; phyllaries 

 in 1 to 3 series, separate, foliaceous in texture; the receptacle high-conic, chaffy 

 throughout; ray flowers absent; disk flowers several, with minute tubular corolla 

 and 5 free anthers and vestigial style and ovary. 



An American genus (now widely distributed) of two dozen species or possibly 

 as few as 2 species depending on the criteria used. The fruits are known to cause 

 mechanical damage to animals while the young herbage, when eaten, is known to 

 be poisonous to pigs. 



1. Most nodes with a trifid yellow lateral spine attached near the base of the 



leaf 1. X. spinosum. 



1. Herbage not armed, only the heads armed 2. X. strumarium. 



1. Xanthium spinosum L. Spiny cocklebur. 



Stems erect or ascending, branching, 2-10 dm. tall, puberulent; leaves lanceo- 

 late, 4-8 cm. long, with a pair of long narrow lobes on lower half of blade, 

 sometimes with a few small lobes above middle, green above, densely white- 

 pubescent on lower surface, shortly petioled, each with a pair of long yellow 3- or 

 4-parted stipular spines at base; fruiting bur weakly spiny, tomentose, about 1 cm. 

 long, the beaks inconspicuous. 



Abundant in waste fields, sometimes along dikes and edges of marshy areas, in 

 our area, summer-fall; occasional throughout the U.S. 



2. Xanthium strumarium L. Abrojo. Fig. 759. 



Stems erect, usually branched, 2-9 dm. tall; leaves thick, harsh, deltoid-ovate, 

 cordate at base or subtruncate, irregularly serrate to somewhat 3-lobed, green on 

 both sides, on petioles as long as blades; fruiting bur 1-2 cm. long, cylindric, 

 densely set with hooked yellowish prickles 3-7 mm. long, these often glandular 

 and sparsely pubescent at base, the 2 beaks strongly developed, hooked at tip. 

 X. orientale L., X. chinense Mill., X. italicum Moretti, X. pensylvanicum Wallr., 

 X. saccharatum Wallr., X. speciosum Kearn., X. cenchroides Millsp. & Sherff. 



Very abundant in low marshy lands and mud flats about lakes; a weed through- 

 out the U.S., nat. to Atl. Coast. 



It seems useless at this point to try to recognize more than one entity in this 

 complex, for all the proposed segregates intergrade completely. 



24. Eclipta L. 



A genus of a few, perhaps only one, species, widespread in the warmer parts 

 of the world. 



1. Eclipta alba (L.) Hassk. Yerba de tago. Fig. 760. 



Annual with taproots and occasionally also rooting at the nodes, to 1 dm. 

 tall but mostly decumbent stems to 1 m. long, throughout with antrorse-appressed 

 stiff hairs about 0.3-0.5 mm. long; leaves opposite, short-petiolate; blades mem- 

 branous, 2-10 cm. long, linear-oblong to narrowly elliptic, usually remotely and 

 obscurely toothed; heads solitary at the ends of short axillary peduncles, about 

 1 cm. high; involucre broadly campanulate; phyllaries in roughly 2 series, outer 



1646 



