Mostly robust plants. Rootstock creeping, mostly 
perennial. Stem erect, grooved, branchless in some spe- 
cies, or with simple or compound, verticillate branches 
in others. Leaves rudimentary, verticillate, united near- 
ly their entire length, forming sheaths at the nodes of 
the stem. 
t+ Stems of one kind. 
* Ridges of the stem with one line of tubercles. 
1. E. praealtum Rafin. Ries: 
Eiquisetum praealium Rafin. 1817. Fl. Lud. 13. 
Lt. robustum A. Br. 1843. Amer. Journ. Sc. 46: 
88 [transl]. by Dr. Engelmann]. aston, in Gray, 
Man. 677. Underw. in Il. Fl. 1: 38; Nat. Ferns 
129; in Britt. Man. 23. Clute, Fern Allies 26. 
ScourinG Rusu. 
Plants sometimes 2 m. or more in height; stems 1 cm. 
or wider at the base and usually simple; sheaths short, 
appressed, marked with two black girdles; teeth caduc- 
ous; spikes ovate, 1 cm. or longer, mucronate. 
Along riverbanks and creeks. 
** Ridges of the stem with two lines of tubercles, 
2. E. hyemale L. Plos. 
Liquisetum hyemale L. Sp. Pl. 1062. Eaton, 1. c. 
677. Underw. in Ill. Fl. 1:38; Nat. Ferns 129; 
in Britt. Man. 23. Cluze, 1. c. 19. 
ScourRInNG Rusu. 
55 
