456 RYDBERG: RocKy MOUNTAIN FLORA 
which is unknown to me, all the North American species are 
closely related to A. Millefolium and may be only forms of that 
species. Notwithstanding the fact that Achillea borealis, on account 
of its large heads and numerous rays, has been placed in the 
Ptarmica section of the genus, it is closely related to A. Millefolium, 
and can be connected with it through two different lines of rela- 
tionship. (See below.) It is very hard to say whether the native 
species of the Millefolium group admitted by Pollard should be 
regarded as species or as varieties of A. Millefolium and my inten- 
tion here is not to express any opinion on that subject. I only wish 
to clear certain points regarding which there seems to be a great 
deal of confusion. I shall here use the specific names that have 
been applied to the different forms, whenever such are available. 
ACHILLEA MILLEFOLIUM L. Sp. Pl. 899. 1753 
This is a native of northern Europe and I think also of northern 
New York and New England and eastern Canada; at least it has 
naturalized itself in that part of North America. Elsewhere it is 
only sparingly introduced. It is a characteristic northern plant. 
It differs from all the other native forms in being less villous and 
having shorter hairs. |The rachis of the leaves is distinctly wing- 
margined and the primary segments more or less decurrent; they are 
usually decidedly spreading. The secondary segments are short, 
lanceolate, and spinulose-tipped. The rays are comparatively 
large, 2-3.5 mm. broad. The bracts have usually brown margins. 
In the far north, the plant often becomes more hairy and the 
margins almost black, and it approaches A. borealis on one hand 
and A. lanulosa on the other. Of such specimens we have one 
from North Iceland, collected by Olasur Davidson, and two col- 
lected by Collins and Fernald, one at Carleton Point, Que., in 
1904 (labeled A. lanulosa) and the other at Mt. Albert, Que., in 
1906, no. 257 (labeled A. borealis). 
Achillea occidentalis Raf.; DC. Prod. 6: 24. 1837, 
as a synonym under 
. Millefolium occidentalis DC. loc. cit. 
- Millefolium Pollard, Bull. Torrey Club 26: 371, in part. 1899. 
Not A. Millefolium L. 175 
3. 
This is evidently the plant that Pollard took for the real 
ee 
