390 COMPOSITAE 
96. ACHILLEA* L. Sp. Pl. 896. 1753. 
Perennial herbs with serrate to tripinnatifid, alternate leaves. Heads several to many, 
aggregated into terminal corymbiform panicles, generally radiate. Involucre campanulate 
to ovoid; bracts Hoth with broad, scarigus, fimbriate margins, in 3-4 unequal series. 
Receptacle conic to c chaffy scales. subtending and nearly sdiun lite the disk- 
flowers. Ray-florets pistillate and fertile; disk-florets perfect. Achenes oblong to ovate, 
strongly obcompressed, callous- margined, glabrous; pappus none. [Name in honor f 
Achilles. ] 
A genus of perhaps 75 species native to the northern hemisphere, mainly in the Old World. Type species, 
caves santolina L. 
r detailed sotormation on the biological variation and cytology of the Achillea millefolium complex, see 
the ence referenc 
Clausen, J., David 
Effect of inh environme on orth American pla 
296-324, 
Clausen, J., David D. Keck, and be dat gy ney: 1948. a aE studies on the nature of species. III. 
a responses of climatic of Achillea. Carnegie Inst. Wash. Publ. No. 581: 1-129. 
Lawrence, Aig: = i ges Chromosome saue in Achillea in relation to geographic distribution. Amer. Journ. 
38-4 
1939, North American types of Achillea millefolium L. Bot. Notiser 1939: 813-16. 
D. ‘Keck, ah Wiliam, eney 1940. Experimental studies on the nature of species. I. 
plants. Carnegie Inst. Wash. Publ. No. 520: 
Bot. 
Turesson, Gote. 
1. Achillea millefélium L. Common Yarrow or Milfoil. Fig. 5671. 
Achillea millefolium L. Sp. Pl. 899. 1753 
Alitubus millefolium Dulac, Fl. Hautes- a 500. 18 
Achillea borealis Bong. Mem. Acad. St. ersb. ‘de 2 oe 1832. 
Achillea lanulosa Nutt. Journ. Acad. = fet ~ 36. 
romatic, rhizomatous to cespitose. i eies sah rv esta the basal petioled, 
Plan 
the cauline prac sh and sessile; heads ~ snared > adiate, aggregated i at to round-topped, 
corymbifor: a Pe few, 3-8, broadly ovate to orb mets - ba te white, Leo AH: 
pink ; ade. flow 15-40, 0 the ae same color as the 1 rays 
A highly sonics ic ¢ bore: 
bluffs to arctic pete niptne comditiona: 
tetraploid, n=18 (=A. lanulosa Nutt.), and the he: ccapiotd, Noo orealis Bong 
pes sind 
Key to Varieties 
Stems stout, 10-20 dm 
sm cespitose fie om a pow. ‘tire a gray, villous - giga 
Plants rhizo erate wit eis orming a hekivals at the base of the stem; herbage dark green, 
uberulent to sparsely v r. puber 
——— generally fe than = amy. me me 
the t inal te t te-] late, densely congested. 
var. litoralis. 
ar. arentcola. 
Hevhawe dark green, marnals villous. 
Herbage gray, ti sely isin? hiccenra 
Leaf ot fleshy, 
Herhaxe gray, Sik tow 
Margins of phyllaries tight brown to black; roots fibrous from slender rhizomes. 
ar. 
me of phyllaries ee brown to straw-colored; nearly cespitose, with short stout Auadien and 
deep central ta r. lanulosa. 
Hertogs assay green, moverately omer 
g to black; stems tawny-villous; lenterements acicular. 
r. borealis. 
Margins of involucral bracts pale greenish white to straw-color 
Leaf-segments 
s oblanceolate, all segments tending to be Aue in the same plane. 
var. millefolium. 
T € = ae. 
aeeere generally ae mm. high. var. pac 
9 mm. high. 
Achillea millefolium var. analdaa ¢ (Nutt.) Piper in Pibee & Beattie, + vais Bee Reg 196. _1901. 
(Achillea tomentosa Pursh, Fl. Amer. Sept. 563. 1814, not A. ntosa L. 1753 ; A. lanulosa Nutt. Journ. 
eae Shona 7: 36. 1834; "A. millefolium lanulosa Piper, Mazam Pe ref 97; 1901: a mien. ge part lanu- 
losa Pi r, Contr. U.S. Nat. Herb. 11: 584. 1906; A. lanulosa a typica Keck > Car ash. Publ. 
No. 520; 99 me) Stems 3-5 dm. high, arising from short stout rhizomes sa cespitose) herb e gray, 
; leav es em. i im 
chillea millefolium var. ects (Rydb ) Garrett, Spri Fl. Wasatch Reg. 101. Ts. 
lanulosa alpicola Rydb. Mem. N.Y. Bot. Gard. 1: 426. esr dk sehen Greene, "Leake Bot. one e Vas. 
ies A, areal’ Bon yes Bull, Torrey Club as 157 : : 
, Man. FI. - 
fusca G. N age sp. alpic t 
ash. Publ. No. 520: 300. 1940.) Stems seers and erect, 0.5-3 dm. high, arising from long slender r 
roots shallow, fibrous, distributed ove whole rhizome system; herbage gray, white-villous; procs 5-1 
* Text contributed by Malcolm Anthony Nobs. 
