EQUISETACEAE. 

 Equisetum arvense L. Field Horsetail. (Fig. 77.) 



Equisetum arvense L. Sp. PI. 1061. 1753. 



Stems annual, provided with scattered stomata, the 

 fertile appearing in early spring before the sterile. 

 Fertile stems 4 / -io / high, not branched, soon wither- 

 ing, light brown, their loose scarious sheaths mostly 

 distant, whitish, ending in about 12 brown acuminate 

 teeth ; sterile stems green, rather slender, 2'-2 high, 

 6-i9-furrowed, with numerous long mostly simple 

 verticillate 4-angled or rarely 3-angled solid branches, 

 the sheaths of the branches 4-toothed, the stomata in 2 

 rows in the furrows ; central cavity one-fifth to one- 

 fourth the diameter of the stem. 



In sandy soil, especially along roadsides and railways, 

 Newfoundland and Greenland to Alaska, south to Virginia 

 and California. Also in Europe and Asia. Ascends to at 

 least 2500 ft in Virginia. An occasional form in which the 

 sterile stem bears a terminal spike is known as var. sero- 

 tinum. Sterile stems sometimes very short and with long 

 prostrate or ascending branches. May. 



2. Equisetum pratense Ehrh. Thicket Horse- 

 tail. (Fig. 78.) 



Equisetum pratense Ehrh. Hanov. Mag. 138. 1784. 



Stems annual, 8 / -i6 / high, with scattered stomata, the 

 fertile appearing in spring before the sterile, branched 

 when old, only its apex withering, the two becoming 

 similar in age; stems rough, 8-2o-ridged with narrow 

 furrows and cylindric or cup-shaped sheaths ; branches 

 straight, rather short, simple, densely whorled, 3-angled 

 or rarely 4~5-angled, solid ; sheaths of the stem with 

 about 1 1 short ovate-lanceolate teeth, those of the branches 

 3-toothed ; rootstocks solid, acutely angled. 



In 'sandy places, Nova Scotia and Rupert River to Minne- 

 sota, and Alaska, south to New Jersey and Colorado. Also in 

 Europe and Asia. July-Sept. 



3. Equisetum sylvaticum L,. Wood Horse- 

 tail. (Fig. 79.) 



Equisefrtm sylvaticum L. Sp. PI. 1061. 1753. 



Stems annual, provided with scattered stomata, the 

 fertile appearing in early spring before the sterile, at first 

 simple, at length much branched and resembling the 

 sterile, only its naked apex withering. Stems usually 

 i2-furrowed, producing verticillate compound branches, 

 the branchlets curved downward ; sheaths loose, cylin- 

 dric or campanulate, those of the stem with 8-14 blunt- 

 ish teeth, those of the branches with 4 or 5 teeth, those of 

 the branchlets with 3 divergent teeth ; central cavity 

 nearly one half the diameter of the stem ; branches and 

 branchlets solid. 



In moist sandy woods and thickets, Newfoundland and 

 Greenland to Alaska, south to Virginia and Michigan. Also 

 in Europe and Asia. May. 



