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Equisetum

 

Horsetail

KingdomPlantaePlants, but not fungi, lichens, or algae (from Stearn’s Botanical Latin)
SubkingdomTracheobiontaVascular plants—plants with a “circulatory system” for delivering water and nutrients
DivisionEquisetophytaHorsetails, which date back to the Devonian era
ClassEquisetopsidaHorsetails, spore-bearing plants related to ferns
OrderEquisetalesLiving horsetails (most are extinct)
FamilyEquisetaceaeLiving horsetails
GenusEquisetumLiving horsetails

About plant names...

Horsetails are an ancient group of plants, little changed over 300 million years. The genus Equisetum means “horse bristles,” and refers to the plant’s unusually high levels of silica, which make it abrasive enough to serve for scouring, sanding, or polishing. Although Equisetum includes all the now-living relatives of these plants, extinct relatives reached 100' (30 m) in height as far back as the Carboniferous era.

Identification: For excellent comparison photos, see sophy.u-3mrs.fr.

Here are comparisons among the horsetails we have so far:

 

Equisetum (Horsetail)

Horsetail (Equisetum) · Equisetum variegatum, variegated horsetail. · 8/21/2003 · Chandos Lake, Ontario, Canada · By Janet Novak

 
Equisetum arvense

Equisetum fluviatile

Equisetum palustre
Common Name

Field Horsetail

Water Horsetail

Marsh Horsetail
Leaves

 

Photo by Enrico Blasutto.

 

Tiny black scale leaves surround each segment of the stem. Cropped from a photo by Luc Viatour.

 

The ring of small black zig-zags are leaves. Photo by Kristian Peters.
Stem Fertile stems, which have no branches, are up to 12" (30 cm) high; sterile stems up to 24" (60 cm), multiply branched, with upward-pointing needle-like branches. 12-48" (30-121 cm) high, stems hollow, easily squeezed, usu. about ¼" (6.3 mm) in diameter. Smoother and hollower than other horsetails. Usually short, less than 24" (60 cm), only about ⅛" (3.2 mm) in diameter, rough (though branches are fairly smooth). Sterile stems have a long thin tip above the branches. Fertile stems are less prominent but topped with cones. Branches begin partway up the plant, usually quite dense, sometimes sparse or absent.
Fruit

 

Fertile stems have cones 1-1½" (2.5-3.8 cm) long in the spring. Photo by Kristian Peters.

 

Cone about 1" (2.5 cm) long, yellowish-green. Photo by joelpk@flickr.

 

About 1" (2.5 cm) long. Photo by Petr Filippov.
Range/ Zones

Habitats Fields, woods, marshes, roadsides, especially damp areas in partial shade Ponds, marshes, slow-moving water Marshes, swamps, banks of streams, wet places
Type Wild Wild Wild
Occurrence   Common, sometimes considered invasive Relatively rare

 

Equisetum description by Thomas H. Kent, last updated 16 Aug 2013.

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Equisetum (Horsetail)

(Equisetum) · 5/2/2010 · Nashua River Rail Trail, Groton Center, Groton, MA
≈ 10 × 15" (26 × 39 cm) Species not yet identified