226 
IOWA ACADEMY OF SCIENCES. 
credited to North America. It is evident that the genus 
in North America is western, the greater number of 
species belonging to the Rockies and the Pacific coast. 
KEY TO IOWA SPECIES. 
1. Flowers hermaphrodite, 2. 
1. Flowers imperfectly dioecious C. arvensis. 
2. Outer iuvolucral bracts prickly pointed, 3. 
2. Outer involucral bracts slightly pointed or not at all. . . . C. muticus. 
8. Leaves hairy underneath, green above. 
a. Involucral bracts all prickly C. lanceolatus 
h . Bracts with a dorsal glutinous ridge. 
ba. Leaves deeply pinnatitid C. discolor. 
hb. Leaves not deeply pinnatifid, rather small heads 
C. altissimus. 
be. Leaves usually not deeply pinnatifid, large heads 
C. Iowensis. 
8. Leaves tomentose both sides, lobes triangular. 
a. leaves deeply pinnatitid, biennial C. undulatus 
b. leaves deeply pinnatifid, perennial C. canescens. 
4. Leaves green, both sides. Inner bract long, acuminate, 
perennial • C. Hillii. 
CNICUS ARVENSIS, Hoffm 
Cnicus arvensis, Hoffm. Peutschl. FI. 1: pt. 2. 130. 
1804. 2 Ed. 
Pursh. FI. Am. Sept 2: 506. 1814. 
A. Gray. Syn. FI. N. Am. 1 : 398. 1884. 
Watson & Coulter. Gray’s Man. 296. 1890. 
6 Ed. 
Cirsium arvense, Scop. FI. Carn. 2: 126. 1772. 2 Ed. 
— DeCandolle. Prodr. 6: 643. 1837. 
Torrey & Gray. FI. N. Am. 2: 460. 1848. 
— Gray Man. 274. 1868. 5 Ed. 
Serratula arvensis, L. Sp. PI. 820. 1753. 
Carduus arvensis, Robs. Brit. FI. 163. 1777. 
Britton & Brown Illust. FI. N. St. H : 489. 
f. 4071. 1898. 
Smooth perennial, spreading by creeping root-stocks, one to three 
feet high, corymbosely branched at the top; stem smooth; leaves lan- 
ceolate, sessile, and deeply pinnatifid, lobes and margins of leaf with 
spiny teeth; heads small, three-fourths to an inch high, bracts 
appressed, the outer with a broad base, inner narrow, all with an 
acute tip, never spiny, somewhat arachnoid; flowers purple, dioe- 
