HORSETAIL FAMILY. 37 
4. Equisetum palustre L. Marsh Horsetail. 
(Fig. 80.) 
x ui 
i 
li 
Equisetum palustre \,. Sp. Pl. 1061. 1753. 
Stems annual, slender, all alike, 10’-18’ long, very 
deeply 5-9-grooved, the grooves separated by narrow 
roughish wing-like ridges, the central canal very 
small; sheaths rather loose, bearing about § subu- 
late-lanceolate whitish-margined teeth ; branches sim- 
ple, few in the whorls, 4-7-angled, always hollow, ° 
barely sulcate, more abundant below than above, their 
sheaths mostly 5-toothed ; spike rather long; stomata 
abundant in the furrows. 
In wet places, Nova Scotia to Alaska, south to Maine, 
western New York, Minnesota and Arizona. Also in 
Europe. July-Aug. 
5. Equisetum littorale Kuehl. Shore Horsetail. (Fig. 81 
Equisetum littorale Kuehl. Beitr. Pflanz. Russ. 
Reichs, 4:91. 1845. 
Stems annual, very slender, all alike, 8/-18/ 
high, slightly roughened, 6-19-grooved, the 
ridges rounded, the central canal one-half to two- 
thirds the diameter; sheaths sensibly dilated 
above, the uppermost inversely campanulate, 
their teeth herbaceous, membranous at the mar- 
gins, narrow, lanceolate ; branches of two kinds, 
simple, some 4-angled and hollow, some 3-angled 
and solid, the first joint shorter or a trifle longer 
than the sheath of the stem; spike short with 
abortive spores, these commonly with no elaters. 
On sandy river and lake shores, Maine and On- 
tario to New Jersey and Pennsylvania, west to Brit- 
ish Columbia. Alsoin Europe. Supposed to bea 
hybrid. Aug.—Sept. 
6. Equisetum fluviatile L. Swamp Horsetail. 
Equisetum fluviatile I,. Sp. Pl. 1062. 1753. 
Equisetum limosum 1,. Sp. Pl, 1062. 1753. 
Stems annual, all alike, 2°-4° high, slightly 
10-30-furrowed, very smooth, usually producing 
upright branches after the spores are formed, the 
stomata scattered. Sheaths appressed with about 
18 dark brown short acute rigid teeth, air cavities 
wanting under the grooves, small under the 
ridges; central cavity very large; branches hol- 
low, slender, smaller but otherwise much like the 
stems, short or elongated; rootstocks hollow. 
In swamps and along the borders of ponds, Nova 
Scotia to Alaska, south to Virginia, Nebraska and 
Washington. Also in Europe and Asia. May-June. 
