An Illustrated Flora of the Northern United States, Canada and the British Possessions/Equisetaceae

by Nathaniel Lord Britton & Addison Brown

Family 8.   Equisetàceae   Michx.   Fl. Bor. Am. 2: 281.   1803.
Horsetail Family.

Rush-like perennial plants, with mostly hollow jointed simple or often much-branched grooved stems, provided with a double series of cavities and usually with a large central one, the branches verticillate, the nodes provided with diaphragms. Rootstocks subterranean. Leaves reduced to sheaths at the joints, the sheaths toothed. Sporanges 1-celled, clustered underneath the scales of terminal cone-like spikes. Spores all of the same size and shape, furnished with 2 narrow strap-like appendages attached at the middle, coiling around the spore when moist and spreading when dry and mature, in the form of a cross (elaters). Epidermis impregnated with silica, rough. Prothallium on the surface of the ground, green, usually dioecious.

The family consists of the following genus:

1.   Equisètum   [Tourn.] L.   Sp. Pl. 1061.   1753.

Characters of the family.  [Name ancient, signifying horse-tail, in allusion to the copious branching of several species.]  Called also Toad-pipe, Tad-pipe.

About 25 species, of very wide geographic distribution. Type species: Equisetum fluviatile L.

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Stems annual; stomata scattered.

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Stems of two kinds, the fertile appearing in early spring before the sterile.

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Fertile stems simple, soon withering; sheaths of branches of sterile stems 4-toothed.

1.

E. arvense.

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Fertile stems branched when old, only the apex withering.

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Branches of the stem simple, their sheaths 3-toothed.

2.

E. pratense.

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Branches compound.

3.

E. sylvaticum.

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Stems all alike; spores mature in summer; branches simple or none.

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Sheaths rather loose; branches usually long; stems bushy below, attenuate upwards.

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Central cavity very small; spike long.

4.

E. palustre.

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Central cavity about one-half the diameter of stem; spike short.

5.

E. littorale.

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Sheaths appressed; branches usually short.

6.

E. fluviatile.

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Stems mostly perennial, evergreen; spikes tipped with a rigid point; stomata in regular rows.

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Stems tall, usually many-grooved.

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Stems rough and tuberculate, prominently ridged.

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Ridges with 1 line of tubercles; ridges of sheath tricarinate; stem stout.

7.

E. robustum.

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Ridges of the stem with 2 indistinct lines of tubercles; ridges of sheath obscurely 4-carinate; stem slender.

8.

E. hyemale.

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Stems not tuberculate; sheaths enlarged upward.

9.

E. laevigatum.

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Stems low, slender, tufted, usually 5-10-grooved.

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Central cavity small; sheaths 5-10-toothed.

10.

E. variegatum.

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Central cavity none; sheaths 3-toothed.

11.

E. scirpoides.

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1.  Equisetum arvénse  L. Field Horsetail.   Fig. 89.
Equisetum arvense L. 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 withering, 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.
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. serotinum. Sterile stems sometimes very short and with long prostrate or ascending branches. Called also Cornfield Horsetail; Bottlebrush, Horse- or Snake-pipes; Cat's-tail. May.

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	2.  Equisetum pratense  Ehrh. Thicket or Meadow Horsetail.   Fig. 90.
	Equisetum pratense Ehrh. Hanov. Mag. 9: 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 11 short ovate-lanceolate teeth, those of the branches 3-toothed; rootstocks solid, acutely angled.
	In sandy places, Nova Scotia and Rupert River to Minnesota, and Alaska, south to New Jersey, Iowa and Colorado. Also in Europe and Asia. July-Sept.

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3.  Equisetum sylváticum  L. Wood Horsetail.   Bottle-brush.   Fig. 91.
Equisetum sylvaticum L. 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, cylindric or campanulate, those of the stem with 8-14 bluntish 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 Iowa. Also in Europe and Asia. May.

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	4.  Equisetum palústre  L. Marsh Horsetail.   Fig. 92.
	Equisetum palustre L. 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 8 subulate-lanceolate whitish-margined teeth; branches simple, 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, Connecticut, western New York, Illinois and Arizona. Also in Europe and Asia. July-Aug. Marsh-weed, Paddock- or Snake-pipes; Cat-whistles.

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5.  Equisetum littoràle  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.

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	6.  Equisetum fluviátile  L. Swamp Horsetail.   Fig. 94.
	Equisetum fluviatile L. Sp. Pl. 1062. 1753. Equisetum limosum L. 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 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.  May-June.  Water Horsetail, Paddock-pipes.

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7.  Equisetum robústum  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 aeries 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.

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	8.  Equisetum hyemale  L. Common Scouring-rush.   Fig. 96.
	Equisetum hyemale L. Sp. Pl. 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. The species consists of numerous races.  May-June.  Called also Horsepipe, Mare's-tail, Shave-grass, Shave-weed, Pewterwort, Rough Horsetail, Dutch-rush, Gun-bright.

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9.  Equisetum laevigàtum  A. Br. Smooth Scouring-rush.   Fig. 97.
Equisetum laevigatum A. Br.; Engelm. Amer. Journ. Sci. 46: 87. 1844.
Stems 1°-5° high, simple or little branched, pale green, annual or persistent, 14~3O-furrowed, the ridges almost 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.
Along streams and rivers, especially in clay soil, Ontario to New Jersey, North Carolina, Louisiana, British Columbia and the Mexican border.  May-June.

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	10.  Equisetum variegàtum  Schleich. Variegated Equisetum.   Fig. 98.
	Equisetum rariegatum Schleich. Cat. Pl. Helvet. 27. 1807.
	Stems slender, perennial, evergreen, 6'-18' long, rough, usually simple from a branched base, commonly tufted, 5-10-furrowed, the stomata borne in regular rows. Sheaths campanulate, distinctly 4-carinate, green, variegated with black above, the median furrow deep and excurrent to the teeth and downward to the ridges of the stem, the teeth 5-10, each tipped with a deciduous bristle; central cavity small, rarely wanting.
	Labrador and Greenland to Alaska, south to Connecticut, western New York, Nebraska and Nevada. Also in Europe and Asia. Consists of several races.  May-June.

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11.  Equisetum scirpoìdes  Michx. Sedge-like Equisetum.   Fig. 99.
Equisetum scirpoides Michx. Fl. Bor. Am. 2: 281. 1803.
Stems perennial, evergreen, very slender or filiform, 3'-6' long, somewhat rough, flexuous and curving, growing in slender tufts, mostly 6-furrowed with acute ridges, simple or branching from near the base. Sheaths 3-toothed, distinctly 4-carinate, the central furrow broad, the lateral narrow, the bristly teeth rather persistent; central cavity entirely wanting.
On moist or wet wooded banks, Labrador to Alaska, south to Pennsylvania, Illinois and British Columbia. Also in Europe and Asia.  May-June.