460 RypDBERG: Rocky MOouNTAIN FLORA 
I have seen no intermediate forms. There are several specimens 
from Utah, Idaho, and Washington which I refer to A. lanulosa, 
though they approach A. californica in the stoutness of the plant 
and the larger heads. From Washington I have seen a specimen 
intermediate between Achillea californica 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. Pl. 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- 
