NEW SPECIES OF XANTHIUM AND 

 SOLIDAGO 



CHARLES F. MILLSPAUGH, M.D. and EARL E. SHERFF, Ph.D. 



XANTHIUM (Tourn.) L. 



In determining certain specimens of Xanthium in the Herbarium of 

 the Field Museum, the writers have found the taxonomic status of this 

 genus, as concerns its various species, to be very unsatisfactory at the 

 present time. Much of the uncertainty in connection with several 

 species arises from the difficulty encountered in the past in identifying 

 the older specific names, names that in a number of cases, at least, were 

 founded upon heterogeneous material (cf. E. L. Greene, Pittonia 4: 58. 

 1899; also T. H. Kearney, Bull. Torr. Bot. Club 24: 575. 1897). 

 Another source of confusion in herbaria has been the erroneous identifi- 

 cation of new and undescribed species with any one of the older, more 

 commonly known species. Still further, we must note the well-known 

 contempt with which common weeds such as Xanthium are so often 

 regarded, a reason that explains the surprisingly small number of 

 herbarium specimens of any one species collected heretofore in a given 

 region. 



In 1842, Wallroth (K. F. W., Beitrage zur Botanik i n : 229; G. G. 

 Walpers, Repert. Bot. Syst. 6: 150. 1846), monographing Xanthium, 

 described five new species for this region of America. One of these, 

 X. xanthocarpum, described as having tripartite spines and coming 

 from fields between Staunton and Charlottesville, Virginia, is easily 

 recognized as being Wallroth's North American segregate from X. 

 spinosum L. Under X. spinosum L., Wallroth 1 included the plants of 

 southern Europe, and indeed Linnaeus himself had understood this 

 species as European ("Habitat in Lusitania, Monspelii." Sp. PI. Edit. 

 II: 1400. 1763). But, more recently, this viewpoint has changed. 

 Thus, the Index Kewensis terms X. spinosum L. "cosmopolitan." 

 And some other authorities (e. g., A. Gray, Synopt. Fl. N. Amer. i n : 

 253. 1884) even treat it as a tropical American species. Wallroth's 

 North American segregate seems to have been ignored uniformly by our 

 manuals, apparently with justice. 



1 We rely upon Walpers' Repertorium (loc. cit.) for Wallroth's diagnoses, etc. 



I 



