Western Yarrow

Achillea occidentalis Raf.; (DC. Prodr. 6: 24, as synonym 1837) Rydb. Bull. Torrey Club 37: 456. 1910.
Achillea selacea Schw. in Keating, Narr. Exp. Long 2: 396. 1824. Not A. setacea Waldst. & Kit.
1802. Achillea Millefolium occidentalis DC. Prodr. 6: 24. 1837.
A perennial, with a creeping rootstock; stem 3-5 dm. high, striate, silkyvillous, mostly simple; leaves thrice pinnatifid, sparingly villous, the lower about 1 dm. long, 1-2 cm. wide, oblanceolate in outline, petioled, the upper lance-oblong, sessile, about 1 cm. wide; rachis merely margined; primary divisions ovate in outline, spreading, the ultimate ones linear and spinulose-tipped; heads numerous, in corymbiform panicles; involucre campanula te, 4 mm. high, 2.5-3 mm. broad, villous; bracts 18-20, in 4 series, aU acutish, the outer lanceolate, half as long as the oblong innermost; margins yellowish or straw-colored; ray-flowers 4 or 5; ligules white, less than 2 mm. long, nearly orbicular; disk-flowers about 20; coroUas yellowish-white, 2.5 mm. long; achenes 2 mm. long, with narrowed margins. (Closely related to the following species.)
Type locality: Illinois.
Distribution: Common from Indiana to Tennessee, Arkansas, Nebraska, and Minnesota, but ranging from Massachusetts to Florida and Colorado.

Achillea laxiflora Pollard & Cockerell, Proc. Biol. Soc. Wash 15: 179. 1902.
A stout perennial, with a rootstock; stem about 5 dm. high, glabrous or sparingly illous; leaves coarsely pinuatifid, the upper 5-6 cm. long, glabrous; divisions cleft or lobed; rachis conspicuously wing-margined; ultimate divisions lance-linear, acute; heads numerous, in loose corymbs, long-pedimcled ; involucre turbinate, about 8 mm. high and 6 mm. broad; bracts about 25, in 4 series, scarious, with green keel, the outer acutish, ovate, the inner obtuse or rounded at the apex; ray-flowers about 5; ligules white, suborbicular, about 5 mm. long; disk-flowers 40 or more; corollas 3 mm. long, yellowish-white; achenes linear, prominently winged towards the apex.
Type locality: Sandia Mountains, New Mexico. Distribution: New Mexico and northeastern Arizona.

Achillea lanulosa Nutt. Jour. Acad. Phila. 7: 36. 1834
Achillea lomenlosa Pvirsh.F. m. Sept. 563. 1814. l>!ot A. tomentosa'L. 1753. Achillea Millefolium lanulosa Piper. Mazama 2: 97. 1901. Achillea lanulosa arachnoidea Lunell, Am. Midi. Nat. 1: 235. 1910.
A perennial, with a creeping rootstock; stem 3-5 dm. high, more or less densely villous, simple, striate; leaves 5-10 cm. long, rarely more than 1 cm. wide, the lower oblanceolate in outline and petioled, the upper sessile and clasping, linear in outline; primary divisions lanceolate in outline, ascending, crowded, the ultimate ones linear, spinulose-mucronate; rachis scarcely margined; beads in flat-topped corymbiform panicles; involucre campanulate, 4-4.5 mm. high, 3-4 mm. broad, villous; bracts about 20, in 4 series, the outer lance-ovate, obtusish, the inner elliptic or oblong, obtuse; margins light-brown; ray-flowers commonly 5; ligules white, 2.5-3.5 mm. long, nearly orbicular, round-lobed; disk-flowers about 20; corollas 2.5 mm. long, yellowishwhite; achenes 2 mm. long, with thick margins.
TvPB locality: Ranks of the Kooskoosky [Clearwater River, Idaho].
Distributio.n: Minnesota and Saskatchewan to Kansas, Chihuahua, California, and British Columbia; occasionally introduced eastward to Ontario.

Achillea nigrescens (E. Meyer) Rj^dberg, sp. nov
Achillea Millefolium nigrescens E. Mever, PI. Labrad. 65. 1830. Achillea borealis Britton, Man. 1013, in part. 1901.
A perennial, with a creeping rootstock; stem 2-4 dm. high, sulcate, villous, often branched above; leaves bior tri-pinnatifid, 5-10 cm. long, 1-1.5 cm. wide, the lower oblanceolate and petioled, the upper lanceolate in outline and broadly sessile; primary divisions ovate in outline and spreading, the ultimate ones lanceolate or oblanceolate and with somewhat callous mucronate tips ; heads in more or less compound corymbiform panicles; involucre campanulate, about 5 mm. high, villous; bracts 20-25, in 4 series, the outer lance-ovate and acutish, the inner oblong and obtuse; margins dark-brown; ray-flowers about 5; ligules white or pinkish, about 3 mm. long, suborbicular ; disk-flowers about 25; corollas about 3 mm. long, yellowishwhite; achenes 2.5 mm. long, with thick margins.
Type LOC.M,tTV: Labrador.
Distribution: Greenland and Newfoundland to Mt. Washington, New Hampshire, Hudson Bay, and Mackenzie; Iceland; apparently also on St. Paul's Island, Alaska. Illustratio.v ; Britt. & Brown, 111. Fl. ed. 2. /. 4555 (as A. borealis).

Achillea angustissima Rydberg, sp. nov
A slender perennial, with a rootstock; stem striate, sparingly long-villous, simple; leaves narrowly linear in outline, bipinnatifid, 5-10 cm. long, 2-4 mm. wide; primary divisions short and crowded, ovate, the ultimate ones short, lanceolate, callous towards the spinulose-mucronate tips; heads many, in rather open flat-topped corymbs; involucre about 4.5 mm. high and 3 mm. broad; bracts sparingly villous, lS-20, in 4 series, lightbrown or straw-colored with margins of the same color, the outer lanceolate, the inner oblong, all acutish; ray-flowers usually 5; ligules white, broadly oval, about 4 mm. long, 2.5-3 mm. wide; disk-flowers 15-20; corollas yellowish-white, 2.5 mm. long; achenes fully 2 mm. long, narrowly margined.
Type collected at Nasqually, Oregon, Wilkes Expedition 41 (Torrey Herbarium; herb. Columbia Univ.).