THISTLE FAMILY 973 



61. A. Abrotanum L. A much branched shrub, 5-10 dm. high; lower leaves 

 petioled, 4-6 cm. long, twice pinnately dissected into linear-filiform divisions, 

 with revolute margins, slightly tomentose beneath ; heads numerous, nodding in 

 leafy panicles with racemiform branches; involucre hemispheric, about 3 mm. 

 high and 5 mm. broad; bracts canescent, the outer linear-lanceolate, the rest 

 broadly oval, scarious; ray-flowers about 10; disk-flowers 15-20. Around dwell- 

 ings: N.B. Mass. N.C. Colo.; escaped from cultivation," native of s Eu. and 

 the Orient. 



62. A. Bigelovii A. Gray. Perennial, with a suffruticose base; stems many, 

 2-3 dm. high, silvery-canescent; leaves linear-cuneate to oblong, mostly 3-toothed 

 at the apex, about 1 cm. long, silvery-canescent; heads numerous in a thyrsi- 

 form panicle; involucres canescent, about 2 mm. high and 1.5 mm. broad, 2-4- 

 flowered; flowers yellow, one, or rarely two, of them pistillate. A. petrophila 

 Woot. & Standl. Rocky banks and canons: Tex. Colo. Utah Ariz. Son. 

 Au-S. 



63. A. cana Pursh. Shrub, 3-30 dm. high; branches strict, canescent; 

 leaves linear or lance-linear, acute at both ends, 1-4 cm. long, silvery-canescent 

 on both sides, or the lower with 2-3 acute teeth or lobes at the apex; heads 

 glomerate, in a leafy panicle ; involucres 5-9-flowered ; outer bracts linear or subulate, 

 the inner oval, all more or less tomentose; flowers yellowish. A. colwribiana 

 Nutt. Plains and hills : Sask. Colo. Utah Ore. Mont. Plain Mont. Au-S. 



64. A. arbuscula Nutt. Low shrub, 1-3 dm. high; branches slender, canes- 

 cent; leaves short-cuneate or flabelliform, 3-lobed or 3-parted, 5-12 mm. long, 

 silvery-canescent, or the uppermost entire; heads rather few, in a spike- or raceme- 

 like panicle; involucres about 4 mm. high and 3 mm. broad, 7-9-flowered; bracts 

 elliptic, at least the outer decidedly tomentose; flowers brownish. Dry moun- 

 tains and high plains: Wyo. Calif. Wash. Submont. Mont. Je Au. 



65. A. spiciformis Osterhout. Shrub, 3-10 dm. high; branches somewhat 

 canescent; leaves oblanceolate or cuneate, 1-3.5 cm. long, 3-toothed at the apex 

 or the upper entire, silvery-canescent; heads comparatively few, in a spike- or 

 raceme-like inflorescence; involucres about 6 mm. high and 5 mm. wide, about 

 ^flowered; bracts imbricate, ovate, at least the outer tomentose; flowers brown- 

 ish. A. Rothrockii A. Gray, in part. Dry plains: Colo. Utah. Son. Mont. 

 Au-S. 



66. A. tridentata Nutt. Shrub, 1-4 m. high, much branched; bark of the 

 old stems shreddy; branches erect, silvery-canescent; leaves cuneate, 1-2 cm. 

 long, 3-toothed (rarely 4-7-toothed) at the apex, or the upper linear-cuneate and 

 entire, silvery-canescent; heads paniculate, numerous; involucres well imbricate, 

 about 4 mm. long and 2 mm. wide, 5-8-flowered; bracts oval-elliptic, at least 

 the outer densely tomentose; flowers yellow or brownish. Dry plains and hills: 

 Neb. Colo. Calif. B.C. Plain Mont. Jl-O. 



67. A. angusta Rydb. A shrub, 1CM2 dm. high, with erect branches; 

 leaves canescent, 2-4 cm. long, 1-4 mm. wide, linear and entire or linear-cuneate 

 and merely 3-toothed at the apex; heads numerous, clustered in leafy panicles; 

 involucre 3.5-4 mm. high, 2 mm. broad; the outer bracts thick, ovate, less than 

 one-fourth as long as the innermost; inner bracts oblong, obtuse, scarious-mar- 

 gined; flowers 4-6. A. tridentata angustifolia A. Gray. Plains: Wash. Ida. 

 Nev n Calif. Son. 



68. A. nova A. Nels. Undershrub, 1-3 dm. high; branches slightly tomen- 

 tose, strict; leaves narrowly cuneate, 0.5-2 cm. long, 3-toothed at the apex, finely 

 silvery-canescent; heads numerous, in a narrow, racemiform panicle; involucres 

 3-4 mm. high, scarcely 2 mm. broad, 2-^-flowered; bracts well imbricate, gla- 

 brate or slightly puberulent, elliptic; flowers light brown. Plains and table- 

 lands: Mont. N.M. Ariz. Ida. Svhmont. Mont. Au-O. 



69. A. tripartita Rydb. Shrub or undershrub, 2-6 dm. high; branches 

 canescent; leaves 3-cleft or 3-parted or the upper entire, silvery-canescent; 

 blades or lobes narrowly linear; heads numerous, in a leafy panicle; involucres 

 about 4 mm. high and 2 mm. broad, 3-6-flowered; bracts well imbricate, the 



