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EQUISETACEAE (Horsetail Family)

References: Hauke in FNA (1993b); Lellinger (1985); Mickel (1979).

A family with a single genus and about 15 species.

Equisetum Linnaeus (Horsetail, Scouring Rush)

A genus of about 15 species, nearly cosmopolitan in distribution.

1. Stems perennial, evergreen, stiff; sterile and fertile stems monomorphic and either unbranched or with 2-3 short and unequal branches per node......2

1. Stems annual, deciduous, the sterile stems flexible; sterile and fertile stems dimorphic or monomorphic, usually branched (often copiously so) but sometimes unbranched or sparsely and irregularly so......3

3. Sterile and fertile stems monomorphic; sterile and fertile stems sparsely and irregularly branched; stem ridges 12-24, indistinct; diameter of the central cavity of the stem about 4/5's of the stem diameter......E. fluviatile

3. Sterile and fertile stems dimorphic; sterile stems copiously branched and green, fertile stems unbranched or branched, green, tan, brown, or purplish; stem ridges 4-18, distinct; diameter of the central cavity of the stem usually less than 3/4's of the stem diameter......4

Equisetum arvense Linnaeus, Field Horsetail. Mt, Pd, Cp (NC, SC, VA): moist streambanks, bottomlands, moist disturbed sites; common. March-April. A circumboreal species, occurring throughout North America. [= RAB, C, FNA, G, S, W; E. arvense var. arvense -- F]

Equisetum fluviatile Linnaeus, Water Horsetail, Pipes. Mt (VA): open calcareous wetlands; rare (VA Rare List). June-August. Circumboreal, south in North America to n. VA, PA, IL, IA, and WA. [= C, F, FNA, G, K, W]

Equisetum hyemale Linnaeus ssp. affine (Engelmann) Calder & R.L. Taylor, Tall Scouring Rush. Mt, Pd, Cp (NC, SC, VA): riverbanks, alluvial floodplains; common (uncommon in NC and SC). May-September. Ssp. affine occurs nearly throughout North America and in Mexico and Guatemala; ssp. hyemale is Eurasian. [= FNA; E. hyemale var. affine (Engelmann) A.A. Eaton -- RAB, C, F, W; including E. hyemale var. robustum (A. Braun) A.A. Eaton -- F; including E. hyemale var. pseudohyemale (Farwell) Morton -- G; including E. hyemale var. elatum (Engelmann) Morton -- G; E. praealtum Rafinesque -- S; Hippochaete hyemalis (Linnaeus) Bruhin ssp. affinis (Engelmann) W.A. Weber]

*Equisetum ramosissimum Desfontaines ssp. ramosissimum, Branched Scouring Rush. Cp (NC): disturbed areas; rare, introduced from the Old World, where it is widespread in Europe, Asia, and Africa. This species was apparently introduced long ago on ship's ballast to Wilmington, New Hanover County,and other southeastern ports, such as Pensacola, FL and New Orleans, LA. It is naturalized on the Wilmington waterfront, persisting in disturbed areas, such as in gravel along railroad tracks. Hauke (1979, 1984, 1992) discusses the occurrence of this species in North America. Ssp. debile (Roxburgh) Hauke occurs in se Asia and southern Pacific Islands; it is not known to be naturalized in North America. [= FNA; E. ramosissimum -- K]

Equisetum sylvaticum Linnaeus, Woodland Horsetail. Mt (VA): seepage swamps; rare (VA Rare List). Circumboreal, south in North America to n. VA, WV, OH, MI, WI, IA, WY, MT, and WA. [= C, F, FNA, G, K; including E. sylvaticum var. pauciramosum Milde -- F, G]

There are old reports, repeated in RAB, and S, of the occurrence of E. laevigatum A. Braun in our area; documentation of these reports is not known. It will key to E. hyemale ssp. affine in the above key, but has the strobilis apex rounded (vs. pointed), and aerial stems annual (vs. perennial).

There are old reports, repeated in RAB, S, and FNA, of the occurrence of E. Hferrissii Clute (pro sp.) [= E. hyemale H laevigatum] in our area; documentation of these reports is not known. E. Hferrissii may be distinguished from E. hyemale var. affine (to which it will key above) by the failure of its cones to produce spores at all or the production of aborted spores (vs. production of normal spores) and most stem sheaths lacking a blackish band well below the teeth (vs. most stem sheaths with a narrow to broad blackish band well below the teeth).

E. Hlitorale Khhlewein ex Ruprecht (pro sp.) [arvense H fluviatile] is reported by FNA for VA. It can be distinguished from E. arvense by its white, mis-shapen spores.

Other species in eastern North America: Equisetum palustre Linnaeus of circumboreal distribution. Equisetum Hlitorale Khhlewein ex Ruprecht (pro sp.), south (allegedly) to VA and WV. Equisetum pratense Ehrhart, south to NJ and NY. Equisetum laevigatum A. Braun. Equisetum variegatum Schleicher ex F. Weber & D. Mohr ssp. variegatum. Equisetum scirpoides Michaux. Equisetum Hmackaii (Newman) Brichan. Equisetum Hnelsonii (A.A. Eaton) J.H. Schaffner.


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Flora of the Carolinas and Virginia, Working Draft of 27 October 1997 -- KEY TO PTERIDOPHYTE GENERA. Alan S. Weakley. The Nature Conservancy, Southeast Regional Office, Southern Conservation Science Department.