5. Equisetum Littorale Kuehl. Shore Horsetail

Fig. 93

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 margins, 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, New Brunswick and Ontario to New Jersey and Pennsylvania, west to British Columbia. Also in Europe. Supposed to be a hybrid. Aug.-Sept.

6. Equisetum Fluviatile L. Swamp Horsetail

Fig. 94

Equisetum limosum L. Sp. PI. 1062. 1753.

Equisetum limosum L. Sp. PI. 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 hollow, 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. Water Horsetail, Paddock-pipes. May-June.

7. Equisetum Robustum A. Br. Stout Scouring-Rush

Fig. 95

Equisetum robustum A. Br.; Engelm. Amer. Journ. Sci. 46: 88. 1844.

Equisetum hyemale robustum A. A. Eaton, Fern Bull. 11: 75. 1903.

Stems perennial, stout, tall, evergreen, 3°-11° high, sometimes nearly 1' in diameter, 20-48-furrowed, simple or little branched. Ridges of the stem roughened with a single series of transversely oblong siliceous tubercles; sheaths short, nearly as broad as long, cylindric, 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. 96

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, Furope and Asia. The rough stems of this and related species are used for scouring floors. The species consists of numerous races. Called also Horse-pipe, Mare's-tail, Shave-grass, Shave-weed, Pewter-wort, Rough Horsetail, Dutch-rush, Gun-bright. May-June.