3 g EQUISETACEAE. 



/. Equisetum robustum A. Br. Stout Scouring-rush. (Fig. 83.) 



Equisetum robustum A. Br.; Engelm. Amer. Journ. 

 Sci. 46: 88. 1844. 



Stems perennial, stout, tall, evergreen, 3-n 

 high, sometimes nearly i' in diameter, 2o-4S-fur- 

 rowed, simple or little branched. Ridges of the 

 stem roughened with a single series of transversely 

 oblong siliceous tubercles ; sheaths short, cylin- 

 dric, appressed, marked with black girdles at the 

 base, and at the bases of the dark caducous 

 teeth ; ridges of the sheath 3-carinate ; branches 

 when present occasionally fertile; spikes tipped with 

 a rigid point. 



In wet places, Ohio to Louisiana and Mexico, west 

 to British Columbia and California. Also in Asia. 

 May-June. 



8. Equisetum hyemale L,. Common 

 Scouring-rush. (Fig. 84.) 



Equisetum hyemale L. Sp. PI. 1062. 1753. 



Stems slender, rather stiff, evergreen, 2 '-4 high, 

 with the stomata arranged in regular rows, rough, 

 8-34-furrowed, the ridges with two indistinct lines 

 of tubercles, the central cavity large, from one-half 

 to two-thirds the diameter ; sheaths rather long, 

 cylindric, marked with one or two black girdles, 

 their ridges obscurely 4-carinate ; teeth brown, 

 membranous, soon deciduous ; spikes pointed ; 

 stem rarely producing branches which are usually 

 short and occasionally fertile ; forms are sometimes 

 found with longer sterile branches. 



In wet places and on banks, especially along rivers 

 and lakes, throughout nearly the whole of North 

 America, Europe and Asia. The rough stems of this 

 and related species are used for scouring floors. May- 

 June. 



9. Equisetum laevigatum A. Br. Smooth 

 Scouring-rush. (Fig. 85.) 



Equisetum laevigatum A. Br. ; Engelm. Amer. Journ. 

 Sci. 46:87. is 44 . 



Stems i-5 high, simple or little branched, pale 

 green, persistent, -i^o-furrowed, the ridges al- 

 most smooth. Sheaths elongated and enlarged 

 upward, marked with a black girdle at the base of 

 the mostly deciduous, white-margined teeth and 

 rarely also at their bases ; ridges of the sheath with 

 a faint central carina and sometimes with faint 

 short lateral ones ; stomata arranged in single 

 series ; central cavity very large, the wall of the 

 stem very thin ; spikes pointed. 



All. UK streams and rivers, especially in clay soil, 

 valley <>f tin- Delaware River in New Jersey and eastern 

 Pennsylvania to North Carolina and Louisiana, west to 

 British Columbia and the Mexican border. May-June. 



