214 IOWA ACADEMY OF SCIENCES. 



148. C. rristdteUa Britton. (C cristata) Schwein. 



Frequent in low woods. 

 1411. C. straminea Willcl. Rare in woods. 



150. C. festucaccaWiWd. (C. straminea hrevior Dewey.) 



Common, and extremely variable. 



151. C. hichiieUii Britton. (C. sfraniinea var, crawei 



Boott.) Common on upland prairies. 



152. C. sychnocepliala Carey. Rare in a marsh east of 



Armstrong; also at Spirit Lake.' A plant very 

 different in appearance from any other Ameri- 

 can species of the genus. 



ARACE^. 



Aris^ma Mart. 



153. A. triphjiUum (L.) Torr. .Jack-in-the-pulpit; 



Indian Turnip. Frequent in rich woods. 



AcoRUS L. 



154. A. calanmsL. Sweet-Hag; calamus-root. Infrequent 



in marshes. 



LEMNACE^E. 



Spirodela Schleid. 



155. S. polyrhiza (L. ) Schleid. {Leuina polyrldza L.) 



Very common, floating on stagnant water, 

 especially in bayous along streams. 

 Lemna L. 



15(1 L. trisulca L. Ponds and marshes; frequent. 



commelinAce.^. 



Tradescantia L. 



157. T. cirginiana L. Spiderwort. Open woods and 



prairies; common. 



pontederiace^. 



Heteranthera R. & P. 



158. H. duhia (Jacq.) Mac M. {Schollera graminea A. 



Gray.) Infrequent; shores of lakes. 



