4G0 Rydberg : Rocky Mountain flora 



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 I have seen no intermediate forms. There are several specimens 



from Utah, Idaho, and Washington which I refer to A. lannlosa, 



though they approach A. calif ornica in the stoutness of the plant 



and the larger heads. From Washington I have seen a specimen 



intermediate between Achillea calif ornica and A. borealis and 



another between A. arenicola and A. borealis. Achillea borealis 



is not found in the Rockies within the United States and A. sub- 



alpina not in British America outside of the Rockies. The only 



specimen which I refer to A. borealis though approaching A. 



subalpina, is from the Canadian Rockies of Alberta. 



Petasites corymbosa (R. Br.) Rydb. comb. nov. 



Tussilago corymbosa R. Br. in Chloris Melv. 21. 1823. 

 Petasites palmata frigida Macoun, Cat. Canad. PI. 1: 553. 1886. 



Not P. frigida (L.) Fries. 1845. 



This has been included in Petasites frigida (L.) Fries, but 

 differs in the deeply lobed leaves, the lobing extending one third 

 to one half the distance to the midrib. It is the more common 

 plant of the Canadian Rockies, known as P. frigida. 



Arnica 



This genus, as represented in western North America is one 

 of the most perplexing, and the last word concerning it is far from 

 being said. I doubt if all the species proposed by Dr. Greene 

 and Professor A. Nelson can be maintained. One of my own, 

 Arnica monocephala, must be regarded as a low broad-leaved 

 form of A. pedunculata, and A. tenuis Rydb. might be an entire- 

 leaved and monocephalous form of A. Rydbergii Greene. On 

 the other hand there are evidently forms of this genus that have 

 not been described. 



Considerable confusion has existed in regard to Arnica Chamis- 

 sonis Lessing and A. mollis Hook. Gray in his Synoptical Flora 

 united the two. In the old Torrey herbarium there are two 

 specimens. One of these bears the printed label " Arnica 

 Chamissonis Lessing, Unalaschka" and was received from St. 

 Petersburg. It is evidently from the original collection. It is 

 a plant of the A. foliosa group, with longer loose villous pubes- 

 cence. We have several specimens similar to it from British 

 Columbia, Alberta, and Saskatchewan and at least one from Mon- 



