36 EQUISETACEAE. 
1. Equisetum arvénse I. Field Horsetail. (Fig. 77.) 
Equisetum arvense I,. Sp. Pl. 1061. 1753. 
Stems annual, provided with scattered stomata, the 
fertile appearing in early spring before the sterile. 
Fertile stems 4’-10’ 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, 
6-19-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 
drostrate or ascending branches. May. 
2. Equisetum praténse Ehrh. Thicket Horse- 
tail. (Fig. 78.) 
Equisetum pratense Ehtrh. Hanoy. Mag. 138. 1784. 
Stems annual, 8/-16’ 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, 8-20 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 11 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.) 
Equisetum sylvaticum ¥,. Sp. Pl. 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 
12-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. 
