GENUS 102. ' 



THISTLE FAMILY. 



12. Senecio canus Hook. Silvery Ground- 

 sel.. Fig. 4621. 



S. canus Hook. Fl. Bor. Am. i : 333. pi. 116. 1833. 



S. Purshianus Nutt. Trans. Am. Phil. Soc. (II) 7: 

 412. 1841. 



Perennial, densely and persistently white- 

 tomentose to the inflorescence ; stems slender, 

 usually tufted, 6'-i8' high. Basal and lower 

 leaves spatulate or oval, entire, or rarely some- 

 what repand, very obtuse, i'-2 r long, narrowed 

 into petioles; upper leaves oblong or spatulate, 

 obtuse or acute, mostly sessile, smaller, entire 

 or dentate ; heads several or numerous, 8"-io" 

 broad, usually slender-peduncled; involucre 

 campanulate, or at first short-cylindric, about 

 5" high, its bracts linear-lanceolate, acute, spar- 

 ingly tomentose, or glabrate, usually with no 

 exterior smaller ones; rays 8-12; achenes gla- 

 brous, at least below ; pappus white. 



In dry soil, Manitoba to North Dakota, Nebraska, 

 west to British Columbia and California. Recorded 

 from Minnesota. May-Aug. 



13. Senecio tomentosus Michx. Woolly 

 Ragweed. Ashwort. Fig. 4622. 



6". tomentosus Michx. Fl. Bor. Am. 2: 119. 1803. 



Perennial, more or less densely and persistently 

 tomentose or woolly-canescent ; stems rather stout, 

 solitary, or sometimes tufted, i-2% high. Basal 

 and lower leaves ovate-lanceolate, oblong or rarely 

 spatulate, long-petioled, erect, very obtuse, 2'-6' 

 long, i'-2' wide, crenate-dentate, narrowed or 

 truncate at the base ; stem leaves few and distant, 

 small, linear-lanceolate or spatulate, crenate or 

 rarely laciniate; heads several or numerous, co- 

 rymbose, mostly long-peduncled, 8"-io" broad; 

 involucre cylindric, or narrowly campanulate, its 

 bracts linear-lanceolate, acute or acuminate, at 

 length glabrate, with or without a few small outer 

 ones; rays 10-15; achenes hispidulous, at least 

 on the angles ; pappus white. 



In moist soil, southern New Jersey to Florida, 

 Louisiana, Texas and Arkansas. April- June. 



14. Senecio plattensis Nutt. Prairie Rag- 

 wort. Fig. 4623. 



S. plattensis Nutt. Trans. Am. Phil. Soc. (II) 7: 413. 



1841. 



Perennial, similar to the preceding species, usu- 

 ally smaller-leaved, lower and less tomentose, or 

 becoming glabrate in age, seldom over ii high. 

 Basal leaves oval, ovate or oblong, some or all of 

 them often more or less pinnatifid, with the termi- 

 nal segment much larger than the lateral ones, 

 trenulate or dentate, long-petioled ; stem leaves 

 mostly smaller than the basal ones, usually pin- 

 natifid ; heads several or numerous, compactly or 

 loosely corymbose, conspicuously radiate. 



Indiana and Illinois to Ontario, North Dakota, Colo- 

 rado, Missouri and Texas. April-June. 



Senecio pseudotomentpsus Mackenzie & Bush, of 

 Missouri, differs in having the basal leaves mostly 

 merely dentate. 



