GENUS 102. THISTLE FAMILY. 543 
12. Senecio canus Hook. Silvery Ground- 
sel. Fig. 4621. 
S. canus Hook. Fl. Bor. Am. 1: 333. pl. 116. 1833. 
S. Purshianus Nutt. Trans, Am. Phil. Soc. (II) a3 
42, Sar, 
Perennial, densely and persistently white- 
tomentose to the inflorescence; stems slender, 
usually tufted, 6-18’ high. Basal and lower 
leaves spatulate or oval, entire, or rarely some- 
what repand, very obtuse, 1'-2’ long, narrowed 
into petioles; upper leaves oblong or spatulate, 
obtuse or acute, mostly sessile, smaller, entire 
or dentate; heads several or numerous, 8-10” 
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. 
= 
a 
mS] / 
/\ 13. Senecio tomentdsus Michx. Woolly 
: Ragweed. Ashwort. Fig. 4622. 
“dS. 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, 1°-23° high. Basal 
and lower leaves ovate-lanceolate, oblong or rarely 
spatulate, long-petioled, erect, very obtuse, 2’-6’ 
long, $2’ wide, crenate-dentate, narrowed or 
truncate at the base; stem leaves few and distant, 
small, linear-lanceolate or spatulate, crenate or 
Zz rarely laciniate; heads several or numerous, co- 
rymbose, mostly long-peduncled, 8’-10” 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 I0-I5; 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 platténsis Nutt. Prairie Rag- 
wort. Fig. 4623. 
S. aoe Nutt. Trans. Am. Phil. Soc. (II) 7: 413. 
I I 
Perennial, similar to the preceding species, usu- 
ally smaller-leaved, lower and less tomentose, or 
becoming glabrate in age, seldom over 13° 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, 
crenulate 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 pseudotomentisus Mackenzie & Bush, of 
Missouri, differs in having the basal leaves. mostly 
merely dentate. 
