I From the Bulletin of the Torrey Botanical Club 39: 301-328. 19 Jy 1912 



Studies on the Rocky Mountain flora — XXVII 



Per Axel Rydberg 



NE'W Vi>}< 



SALICACEAE OOTa.\«c^ 



POPULUS HASTATA Dode, Extr. Mon. Gen. Populus (Mem. Soc. 

 Hist. Nat. Autun i8:) 64. 1905 



Some years ago we were forced to admit one of Dode's species, 

 P. Sargefitii. I say forced, because Dode's paper is presented 

 in such an unscientific way that any one might feel incHned to 

 ignore it altogether. His differentiations are based wholly on the 

 leaf forms, and in very few genera do the leaves show so great 

 variation as in Populus. In working over Mr. Butler's collection of 

 Montana plants I found numerous specimens of a poplar which 

 has usually been regarded as P. halsamifera L., sometimes as 

 P. trichocarpa T. & G. A study of the fruit shows that this poplar 

 has the sessile and 3-carpellary fruit and the large involucral cup 

 of P. trichocarpa, but the capsule is proportionally longer than in 

 that species and perfectly glabrous. The eastern P. halsamifera 

 has evident pedicels and almost always 2-carpellary ovary and 

 much smaller involucral cup. The leaves are usually broader 

 than in P. halsamifera and often subcordate at the base. They 

 resemble much those of P. candicans Ait. in outline but are per- 

 fectly glabrous. P. candicans has also pediceled and 2-carpellary 

 capsules. It is apparent that this species represented by Butler's 

 material is P. hastata of Dode, for he associated it with P. tricho- 

 carpa and pointed out just the characters by which it differs from 

 that species. The name hastata was given in reference to the 



301 



