418 Compositaceae 
AA. Heads corymbose, 2—5 cm. wide. W. 
A. lappa L. (Great Burdock) 
SAUSSUREA SAW-WORT . 
Ours 6—18 dm. high. Leaves not prickly. Heads medium-sized, many-flowered; 
involucre-bracts imbricated, in 4—9 series (ours), blunt, obtuse, unappendaged; recep- 
tacle naked or chaffy. Flowers perfect, 5-cleft, blue or pink or purple, the outer filaments 
glabrous, distinct. Akenes glabrous. Pappus of 2 whorls of bristles, the outer rigid, 
short, denticulate, the inner plumose. (Honor of H. B. de Saussure, a Swiss botanist. ) 
WACrE S. americana Hat. 
CARDUUS THISTLE 
Stout, erect. Leaves somewhat prickly, pinnately-veined and often -lobed. Heads 
rayless, large or medium, all alike (or dioicous in A. arvensis), many-flowered; involucre 
cylindric to globose; its bracts mostly narrow, in several series, often spiny. Receptacle 
flat, fleshy, densely bristly. Flowers perfect, fertile, white to red or rarely yellowish. 
Filaments distinct, usually hairy. Akenes glabrous, obovate or oblong, somewhat flat- 
tish, attached at very base. Pappus-bristles many, rather rigid, plumose, long, in | 
whorl, united into a ring at base. (The Latin name; said to be from Celtic ard=a 
sharp point. ) 
A. Perennial by spreading horizontal rootstocks; heads 15-25 mm. high, dioicous. 
W. E. C. arvensis Robs. (Canada Thistle) 
AA. Biennial; heads larger, all alike. 
B. None of the involucre-bracts spine-tipped, all with dilated fringed tips. W. E. 
A, americanus Gr. 
BB. Outer involucre-bracts spine-tipped, inner ones not. 
C. _ Involucre-bracts not at all glandular on the back. 
D._ Involucre-bracts either nearly equal or some with spreading herbaceous tips. 
E. Flowers cream-colored. W. C. E. 
C. remotifolius Hook. 
EE. Flowers white to red. 
F. Plant very white-woolly. U. 
C. occidentalis Nutt. 
FF. Plant densely pubescent to glabrate. 
G. Inner involucre-bracts with dilated tips. E. 
; C. magnificus Nels. 
GG. None of the involucre-bracts with dilated tips. 
H. Herbage pubescent, grayish or green; leaves weakly prickly; 
10—30 dm. high. W. C. E. 
C. edulis Gr. (Edible Thistle) 
HH. Herbage glabrate, green; leaves strongly prickly; 6—9 dm. 
high. E. C. hallii How. 
DD. Involucre-bracts much shorter outward, appressed. 
I. Heads oblong or cylindric; inner involucre-bracts purplish. E. 
C. andersoni Gr. 
II. Heads wider; inner involucre-bracts not or very slightly purplish. 
J. Stem somewhat woolly; inner involucre-bracts somewhat dilated. Es: 
C. foliosus Hook. 
JJ. Stem glabrous; inner involucre-bracts not at all dilated. E. 
C. drummondii Cov. 
CC.  Involucre-bracts with glandular ridge or spot on the back. 
