THISTLE FAMILY 967 



mentulose, 3-5-flowered; sterile central flowers 1-3. A. plattensis Nutt. Plains: 

 Neb. Tex. Ariz. Nev.; Mex. Son. Plain. Ap-O. 



12. A. pedatifida Nutt. Perennial, with a thick woody cespitose caudex; 

 stems 5-15 cm. high, finely canescent; leaves mostly basal, once or twice ternately 

 divided into linear or narrowly spatulate divisions, finely white-tomentulose ; 

 heads few in a spicate or racemose inflorescence, 12-15-flowered; involucres 3-^4 

 mm. broad, tomentose; bracts elliptic; flowers brownish. Arid ground: Wyo. 

 Mont. Ida. Submont. Je Au. 



13. A. Absinthium L. Shrubby; stem 5-15 dm. high, finely canescent; 

 leaves 5-12 cm. long, once to thrice pinnately divided into oblong or lanceolate, 

 obtuse divisions, finely canescent, especially beneath; heads numerous in a large 

 panicle, with racemiform branches, nodding; involucres 4-5 mm. broad, canes- 

 cent; outer bracts linear, the inner oval, scarious-margined. Waste places and 

 around dwellings: Newf. N.C. Mont.; escaped, native of Eu. Au-S. 



14. A. frigida Willd. Perennial, with a cespitose, suffrutescent caudex; 

 stem 2-5 dm. high, finely canescent; leaves twice pinnatifid, with linear-filiform 

 divisions, silvery-white, in age often turning brownish; heads numerous, race- 

 mosely disposed, nodding; involucres 4-6 mm. broad, canescent or tomentose; 

 bracts oblong or lanceolate; corollas yellow, glabrous. Dry plains and hills: 

 Hudson Bay Tex. Ariz. Ida. Alaska; Asia. Plain Mont. Jl-O. 



15. A. scopulorum A. Gray. Perennial, with a cespitose caudex; stem 

 simple, canescent, 1-2 dm. high; lower leaves petioled, 3-7 cm. long, bipinnatifid, 

 with linear or oblong divisions, silky-canescent ; upper stem-leaves small and 

 less divided; heads 3-12, spicately or racemosely disposed, 18-30-flowered; invo- 

 lucres 6-8 mm. broad; bracts oval, tomentose, black- or brown-margined; corollas 

 yellow, hirsute at the summit. High mountains: Mont. N.M. Utah. Sub- 

 alp. Alp. Jl-S. 



16. A. Pattersoni A. Gray. Perennial, with a cespitose caudex; stem white- 

 tomentose; lower leaves pinnatifid, with 3-5 linear divisions, sericeous; upper 

 stem-leaves linear, entire or 2-3-cleft at the apex; heads 1-5, usually conglomer- 

 ate, 8-12 mm. broad; bracts oblong or elliptic, white-tomentose with brown or 

 black margins; flowers yellow, 40-50, the central ones fertile; receptacle villous. 

 Alpine peaks: Colo. Subalp. Alp. Jl-Au. 



17. A. biennis Willd. Biennial; stem 3-10 dm. high, glabrous; leaves pin- 

 nately or bipinnately parted into lanceolate, laciniate-dentate divisions, gla- 

 brous; heads small, numerous, in a dense leafy panicle; involucres 2-3 mm. wide, 

 glabrous; bracts elliptic, dark-green, scarious-margined; corollas yellow, glabrous. 

 Wet places: N.S.N.J. Calif. B.C. Mack. Plain Mont. Au-D. 



18. A. minuta Rydb. A low undershrub, woody at the base; stems 1 dm. 

 high or less, at first slightly tomentose, in age glabrate and reddish; leaves mostly 

 basal, silvery-silky, about 1 cm. long, pinnatifid, with 5-7 narrowly oblanceolate 

 approximate divisions; stem-leaves smaller, with linear-filiform divisions; in- 

 florescence simple, spike-like, 2-^4 cm. long; involucre hemispheric, 2.5 mm. high; 

 bracts about 10, light brown, slightly tomentose, in age glabrate, ovate, acutish, 

 scarious-margined. Plains: Alta. Plain. 



19. A. Tyrrellii Rydb. Tufted perennial; stems 2-3 dm. high, densely 

 silky-canescent; leaves 1.5-3 cm. long, white-silvery on both sides, the basal ones 

 twice pinnatifid, with 3-5 crowded primary divisions, which are 3-5-cleft into 

 oblanceolate or spatulate divisions; upper leaves ternate to entire and linear; 

 heads racemose, nodding; involucre hemispheric, about 5 mm. high and 7 mm. 

 broad; bracts 12-15, elliptic, densely canescent on the back, with conspicuous 

 dark brown scarious margins; ray-flowers about 10; disk-flowers about 30. 

 Mountains: B.C. Subalp. S. 



20. A. saxicola Rydb. Perennial, with a cespitose caudex; stem decumbent 

 at the base, 1-3 dm. high, loosely villous; basal leaves petioled, 2-8 cm. long, 

 twice pinnately parted into lanceolate divisions, loosely villous; heads several, 

 racemosely disposed, some of them, at least the lower, on long erect peduncles, 

 nodding; involucres 8-10 mm. broad, villous; bracts elliptic with black or dark 



