VOL. XVI, PP. 9-10 FEBRUARY 21, 1903 



PROCEEDINGS 



OF THK 



BIOLOGICAL SOCIETY OF WASHINGTON 



A NEW COCKLEBUR FROM NEW MEXICO. 



BY T. D. A. COCKERELL. 



My work on the plants of the region about Las Vegas has 

 brought to light the interesting form of Xanthium commune 

 Britton, described below. The first specimens collected were 

 referred to Prof. E. O. Wooton, who was then working at Col 

 umbia University. He found that nothing of the kind was 

 represented in the Columbia herbarium and concluded that the 

 species was new. Upon his return to New Mexico I urged him 

 to publish it, but he delayed, and after a couple of years we 

 both became doubtful of the validity of the species, observing 

 that nothing but the burs would separate it from X. commune 

 (then called by us X. canadense). Later our doubts were con 

 firmed when I found at Las Vegas a pair of burs, one of each 

 kind, growing on the same twig. This specimen is now in the 

 herbarium of the Agricultural College at Mesilla Park. Among 

 hundreds of plants since observed, I have not seen another like 

 it, nor have I seen a plant which could not at once be referred 

 to one or the other form. 



Xanthium commune wootoni, sp. nov. 



Similar in all respects to X. commune Britton, but the burs more slen 

 der (greatest transverse diameter about 6 mm., beaks and prickles about 

 4~paoc. BIOL. Soc. WASH. VOL. XVI, 1803. (9) 



