THISTLE FAMILY 961 



Plant shrubby, 2-4 dm. high, glabrous; heads several, corymbose. 1. S. diver sifolia. 

 Plant with cespitose caudices, 1.5 dm. or less high, silvery-canescent ; heads solitary or 



in a small cluster. 

 Heads few, clustered. 



Heads more or less peduncled ; basal leaves obovate-cuneate, with 3-5 round lobes 



at the apex. 2. S. argentea. 



Heads sessile hi a capitate cluster; basal leaves once or twice ternately divided 



into linear or oblong divisions. 3. S. capitata. 



Heads S9litary; basal leaves simple, linear, or ternately cleft at the apex into linear 

 divisions. 4. S. simplex. 



1. S. diversifolia (D. C. Eat.) Rydb. Undershrub 2^ dm. high; stem gla- 

 brous, leafy; lower leaves pinnatifid, with linear divisions, glabrous, the upper 

 narrowly linear and entire; involucres hemispheric, 5-6 mm. broad, glabrous; 

 bracts broadly ovate, with erose, white-scarious margins; marginal pistillate 

 flowers 8-10. Tanacetum diversifolium D. C. Eat. Canons: Utah. Submont. 

 Jl-Au. 



2. S. argentea Nutt. Stem 5-15 cm. high, silvery-canescent; leaves cuneate 

 or flabelliform, 5-12 mm. long, 3-6-toothed or -lobed at the apex, silvery-canes- 

 cent, or the uppermost oblong or linear, entire; heads few, corymbose; involucres 

 hemispheric or campanulate, 3-5 mm. broad; bracts obovate, slightly tomentose 

 when young, yellowish, with broad erose scarious margins; marginal pistillate 

 flowers about 5. T. Nuttallii T. & G. Barren hills: Mont. Wyo. Submont. 

 My-Je. 



3. S. capitata Nutt. Stem 5^-15 cm. high, silvery-canescent; leaves mostly 

 basal, ternately or bi-ternately divided into linear divisions, silvery-canescent; 

 heads 8-15; involucre 4-5 mm. broad; bracts tomentose, yellowish, obovate, 

 erose; marginal pistillate flowers about 5. T. capitatum T. & G. Dry hills: 

 Mont. Wyo. Submont. My-Jl. 



4. S. simplex (A. Nels.) Heller. Leaves mostly basal, silvery-canescent, 

 simple and linear or 2-3-cleft, with linear divisions, only 2-3 cm. long; stem 5-12 

 cm. high; heads solitary, 8-10 mm. broad, hemispheric; bracts obovate, slightly 

 canescent, yellowish; pistillate marginal flowers few. T. simplex A. Nels. Dry 

 hills: Wyo. Submont. My-Je. 



122. PICROTHAMNUS Nutt. 



Low spiny shrubs. Leaves alternate, pedately divided and again lobed, with 

 narrow divisions. Heads solitary or in small racemes, apparently discoid, the 

 marginal flowers without ligules. Involucre saucer-shaped; bracts obovate- 

 cuneate, scarious, in two more or less distinct subequal series; receptacle naked. 

 Marginal flowers (functionally ray-flowers) few, pistillate, fertile; corolla short, 

 deeply 2-cleft, villous; style long-exserted, with long linear obtuse branches. 

 Disk-flowers hermaphrodite but sterile; corollas with a narrow obconic tube, a 

 turbinate throat, and a 5-lobed limb, densely arachnoid-hairy; anthers oblong, 

 with subulate tips and obtuse bases; style slender, with a peltate, erose stigma. 

 Achenes ellipsoid, densely arachnoid-hairy. 



1. P. desertorum Nutt. Spiny undershrub; stem villous-tomentose, 1-5 

 dm. high; leaves pedately 5-parted and again 3-lobed, with spatulate divisions, 

 villous. Artemisia spinescens D. C. Eat. Desert regions: Wyo. N.M. e Calif. 

 Ore. Plain Submont. 



123. ARTEMISIA L. WORMWOOD, MTJGWORT, CUDWEED, SAGE BRUSH. 



Perennial or annual herbs, or shrubs, usually bitter-aromatic. Leaves alter- 

 nate. Heads small, most commonly panicled and nodding when young, ap- 

 parently discoid; the marginal flowers without ligules or wanting. Involucre 

 campanulate to hemispheric; bracts in 2^-4 series, at least the inner ones more or 

 less scarious. Receptacle naked or hairy, convex or conic. Marginal flowers 

 (functionally ray-flowers) pistillate and fertile or wanting; corollas cylindric or 

 subcylindric and somewhat tapering upwards, 2-3-, rarely 4-toothed, often some- 

 what oblique; style more or less exserted, 2-cleft; style-branches linear-filiform 

 and subterete to oblong and somewhat flattened. Disk-flowers hermaphrodite, 



