THISTLE FAMILY 871 



and scabrous-ciliolate on the margins, densely hispidulous-puberulent beneath; 

 inflorescence short-conic; involucre about 3 mm. high; bracts linear-acute; 

 achenes sparingly hispidulous. S. scabriuscula Rydb., in part. Dry soil: Sask. 

 Mo. Tex. Mont. Plain. Jl-S. 



21. S. pruinosa Greene. Stem about 1 m. high; leaves ascending, about 5 

 cm. long, elliptic-lanceolate, acute or acuminate, lightly but evenly serrate, 

 3-ribbed, canescent on both sides, with a dense and soft pubescence ; inflorescence 

 short-pyramidal; outer bracts linear-subulate, the inner oblong, lance-obtuse. 

 Plains: Sask. Plain. Au. 



22. S. gilvocanescens (Rydb.) Smyth. Stem slender, 3-6 dm. high, puberu- 

 lent; leaves 3-6 cm. long, sparingly serrate or entire, puberulent-canescent; in- 

 florescence small and dense; heads 3-4 mm. high; bracts narrowly linear, acute; 

 achenes sparingly hairy. Sandy soil: Minn. Kans. Utah Mont. Plain. 

 Jl-Au. 



23. S. Garrettii Rydb. Stem 2-3 dm. high, sparingly puberulent or gla- 

 brous; leaves obovate-spatulate or the upper oval, entire or the lower toothed 

 towards the apex, rather thin, minutely and sparingly scabrous-puberulent, 

 scabrous-ciliolate, 3-6 cm. long; inflorescence more or less leafy, with a few 

 secund branches; heads 5-6 mm. high; bracts lanceolate, acute, yellowish; 

 achenes sparingly hirsute. Canons: Utah Wyo. Submont. Au. 



24. S. nana Nutt. Stem finely canescent-puberulent, 1-2 dm. (rarely 3 

 dm.) high; basal leaves 2-6 cm. long, petioled, canescent-puberulent, spatulate, 

 rounded at the apex, entire or crenulate; stem-leaves oblanceolate; heads 5-7 

 mm. high; achenes strigose. High dry plains: Mont. Colo. Ariz. Submont. 

 Mont. Jl-S. 



25. S. nivea Rydb. Stem 1-2 dm. high, canescent-puberulent; basal leaves 

 2-4 cm. long, short-petioled, obovate-spatulate, rounded at the apex, entire or 

 nearly so, canescent-puberulent, almost velvety and almost white; stem-leaves 

 oblanceolate; heads about 6 mm. high; achenes hirsute-strigose. Dry hillsides: 

 Mont. Submont. Jl-Au. 



26. S. pulcherrima A. Nels. Stem 3-8 dm. high, striate, cinereous-puberu- 

 lent; lower leaves narrowly oblanceolate, entire, 6-12 cm. long; upper leaves 

 oblong or linear; all cinereous-puberulent; heads about 6 mm. high; achenes 

 puberulent. S. diffusa A. Nels. Dry plains: Sask. Minn. Neb. Colo. 

 Ariz. Alta. Plain Mont. Jl-S. 



27. S. radulina Rydb. Stem 3-4 dm. high, grayish-puberulent; lower 

 leaves obtuse, crenate at the apex, finely puberulent; heads about 4 mm. high; 

 bracts oblong, obtuse, or the inner linear; achenes hirsutulous. Mountains: Utah 



Colo. Submont. Au. 



28. S. trinervata Greene. Stem decumbent at the base, cinereous-puberu- 

 lent, 3-6 dm. high; leaves oblanceolate, 5-10 cm. long, puberulent, scabrous- 

 ciliolate on the margins, entire or nearly so; heads about 6 mm. high; achenes 

 hispidulous. Plains and hills : S.D. N.M. Ariz. Utah. Submont. Mont. Jl-S. 



29. S. mollis Bartl. Stem 2-4 dm. high, cinereous-puberulent, strict, leafy; 

 leaves obovate, oval, or broadly spatulate, or the upper elliptic, canescent, the 

 lower more or less serrate; panicle usually dense and somewhat leafy; heads 5-7 

 mm. high; achenes sparingly hirsutulous. S. nemoralis incana A. Gray. Dry 

 plains: Sask. Tex. Colo. Mont. Plain Submont. Jl-S. 



30. S. Wardii Britton. Stem 4-10 dm. high, puberulent; leaves lanceolate 

 or ovate-lanceolate, entire or with a few teeth, firm, 5-9 cm. long, pale, usually 

 shining, scabrous-puberulent; panicle narrow, leafy; heads about 8 mm. high; 

 bracts lanceolate, acute, canescent, squarrose. Plains and prairies: Mo. Ark. 

 Okla. w Neb. Plain. Au-O. 



26. PETRADORIA Greene. ROCK GOLDENROD. 



Low tufted perennial herbs, with a short branched caudex. Leaves alternate, 

 entire, 3-nerved and punctate. Heads small, several, corymbose. Involucres 

 cylindraceous; bracts in more or less distinct rows, rigid, somewhat carinate, 



