226 low A 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 involucral 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 



b. Bracts with a dorsal glutinous ridge. 



ba. Leaves deeply pinnatitid C. discolor. 



bb. Leaves not deeply pinnatitid, rather small heads 



C. altissimus . 



be. Leaves usually not deeply pinnatitid, large heads 



C. lowensis. 



8. Leaves tomentose both sides, lobes triangular. 



a. leaves deeply pinnatitid, biennial C undulatus 



b. leaves deeply pinnatitid, perennial C. canescens. 



4. Leaves green, both sides. Inner bract long, acuminate, 



perennial • C. Hillii. 



CNICUS AUVENSIS, Hoffm 



Cnicus arvensis, Hoffm. J>eutschl. Fl. 1: pt. 2. 130. 



1804. 2 Ed. 



Pursh. Fl. Am. Sept 2: 506. 1814. 



A. Gray. Syn. Fl. N. Am. 1 : 398. 1884. 



Watson & Coulter. Gray's Man. 296. 1890. 



6 Ed. 

 Cirsium arvense, Scop. Fl. Carn, 2: 126. 1772. 2 Ed. 



DeCandolle. Prodr. 6: 643. 1837. 



Torrey & Gray. Fl. N. Am. 2: 460. 1848. 



Gray Man. 274. 1868. 5 Ed. 



Serratula arvensis, L. Sp. PI. 820. 1753. 



Carduus arvensis, Robs. Brit. Fl. 163. 1777. 



Britton & Brown Illust. Fl. N. St. H: 489. 



/: 4:{y71. 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 pinnatitid, lobes and margins of leaf with 

 spinv 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- 



