APRIL, 1919. XANTHIUM MILLSPAUGH AND SHERFF. 43 



rini." This is clearly one of Moretti's original specimens. In the 

 De Candolle Herbarium at Geneva there exists a fine mature specimen 

 collected by Moretti in the vicinity of Pavia, in 1819. This likewise 

 had been labeled Xanthium echinatum by Moretti. 1 It matches well 

 the Turin specimen from the Bernhardi Herbarium and both of these 

 specimens agree perfectly with the plate published (from a specimen 

 sent by Moretti) by Reichenbach (loc. tit.) in 1826.* 



X. varians Greene, while somewhat atypic in that its fruiting prickles 

 are slightly stouter, is easily seen to be a form of this species. X. 

 Macounii Britton is best considered as likewise a form of X. italicum. 

 Unfortunately, the single type specimen on which the description of 

 X. Macounii was based has immature fruits. These point, however, 

 to a somewhat atypic, rather sparsely aculeate form of X. italicum, 

 such as may be found growing occasionally among plants of the typical 

 form. Of X. glandulijerum Greene we have seen two specimens of the 

 type collection (Hb. Can.; Hb. Greene 19844). These would seem at 

 first to be closer to X. echinatum Murr. But the size and shape of the 

 achene and the character of the foliage all indicate a closer affinity with 

 X. italicum. At best, X. glandulijerum is probably to be considered as 

 only another of the mutant forms produced occasionally by X. italicum. 



With X. italicum must be placed also X. commune Britton, originally 

 described from Westport, New York. The type specimen of X. com- 

 mune has the burs somewhat immature. These match closely those of 

 the type material of X. glandulijerum Greene. We have seen several 

 cases (e. g., Greenman 537, Hb. Gray) in which exactly the same form of 

 burs appeared along with other burs that were topical of X. italicum. 

 But whether this divergence from the typical form was due to hybridiza- 

 tion or to mere variation we are unable to state. 8 



18. XANTHIUM ACEROSUM Greene, Pittonia 4: 63. 1899. 



Caulis flexuosus, lineis purpureis longitudinalibus saepe maculatus. 

 supra scaber, infra fere glabrescens, verisimiliter circum 4-9 dm. altus, 

 Folia late subcordato-ovata, obtusa, crenato-dentata, utrinque setulis 

 minutis adpressis scabra, petiolis adjectis 0.7-2 dm. longa, petiolis 

 laminis subaequantibus. Fructuum (PI. VII, f. *8; PI. IX, ff. 22-24) 

 corpus cylindricum, moderate glanduloso-pubescens, aculeis subremotis 

 armatum, 1.5-1.9 cm. longum et 6-7 mm. crassum; rostris tenuibus, 

 attenuatis, molliter pubescentibus, subrectis aut irregulariter incurvatis, 

 ad apicem minime hamosis, 7-8 mm. longis; aculeis vix numerosis, 



1 We rely upon a large and excellent photograph of the sheet, furnished us through 

 the great kindness of the late M. Casimir De Candolle. 



J We have seen various European specimens collected, since Moretti's time, in 

 Italy, Corsica, Sardinia etc. Some of these were already labeled X. italicum. 



1 For distinctions between X. italicum and X. pennsylvanicum, see p. 34. 



