General Species Description
- Giant horsetail is an annual herb with dimorphic stems. Separate fertile and sterile or vegetative stems are joined
together by underground rhizomes. The aerial stems are erect, ribbed, hollow, and have interlocking segments.
The cells walls are impregnated with silicon dioxide crystals, causing the plants to feel rough and gritty.
Sheaths with persistent teeth, modified leaves, grow around each joint. The fertile stems are permanently whitish or
brownish (mostly non-photosynthetic), 25-60 cm tall, 1-2.5 cm thick, unbranched and terminated with a strobilus (cone).
The greenish-brown sterile stems lack cones and have fine, jointed, horizontal to descending branches developing in whorls
from the nodes between
stem segments. They grow to 3 m tall and 2 cm thick, have 14-40 ridges and a central cavity 2/3 to 3/4 of the diameter
of the stem. The perennial rhizomes have adventitious roots arising at the nodes. The rhizomes are black, covered in
felt-like hairs, and may have pear-shaped tubers at the joints. Giant horsetail is the largest of the common dimorphic
horsetails, explaining its common name. Locally, our giant horsetail is the variety braunii.
- The leaves are reduced, darkened, bract-like teeth located atop a tubular sheath that is whorled around each stem
joint. Fertile stem sheaths are 2-5 cm long with 20-30 long teeth connate in groups of 2-4. Sterile stem sheaths are
1-2.5 cm long with 14-40 teeth 3-8 mm long; they are pale below and dark above.
- Equisetum species have no flowers. Microscopic gametophyes are the site of gamete production and
- The reproductive structures of Equisetum species are hollow, blunt strobili growing on the tips of
fertile stems. The cones of E. telmateia are 4-10 cm long and consist of a central axis to which aggregates of
sporgangiophores are attached. These sporangiophores bear sporangia, each containing numerous spores. The spores are
green, small and uniform in size, and have 4 thread-like elaters for dispersal. Fertile stems arise early in the spring
prior to the sterile stems, and wither soon after the spores are released.
- Giant horsetail is found at low to middle elevations usually near standing or flowing water. Dense colonies often
form in moist forests and meadows, stream banks, swamps, seepage areas and gullies, giving the landscape a delicate
texture. Like most Equisetum species, E. telmateia also inhabits disturbed areas such as roadsides and
gravel ditches. This species is often found in association with wetland grasses, sedges and rushes, forming a dense
- This species is found in western North America from Alaska to southern California. On the Pacific Coast, it is
only found as north as the tip of Vancouver Island, except for the Queen Charlotte Islands. Although it is found in
many counties in the Pacific Northwest, giant horsetail is not as widespread as the other common horsetails.
- Although all vegetative horsetail stems look fairly similar, especially from a distance, giant horsetail is the
tallest of the common dimorphic horsetails. Field horsetail (Equisetum arvense) has
similar looking fertile and sterile stems, but they are much narrower
and shorter, and generally less robust. Another way to distinguish smaller specimens of giant horsetail from field
horsetail is the former has larger, looser sheaths with more teeth. The fertile stems of giant horsetail may be confused
with the unbranched, monomorphic fertile stems of scouring rush (E. hyemale). However, scouring rush is an evergreen
perennial and have sharp-pointed cones that are only 2.5 cm long.
- Giant horsetail is indigestible to wildlife due to the silicon dioxide crystals.
- This species was the most preferred Equisetum species of coastal native peoples as an important springtime
vegetable. The young fertile and vegetative shoots were picked, de-sheathed and eaten raw. However, this genus has
been known to be poisonous to livestock and humans if eaten in large quantities. Some native peoples also picked the
tops of these plants, boiled them, and drank a glassful of the liquid to cure a urinary ailment. E. telmateia was
one of the many Equisetum species used as medicine to treat burns; the stems were burned and the ashes applied
to the wound. The silicon dioxide crystals make Equisetum species great scouring tools. Native peoples used
them extensively for smoothing and polishing wood and soapstone. In fact, modern-day hunters and outdoors people still
use them as scouring utensils for cleaning pots and pans.
- Cooke, S. S., ed. 1997. A Field Guide to the Common Wetland Plants of Western Washington & Northwest Oregon.
Seattle Audubon Society and Washington Native Plant Society. Seattle Audubon Society, Seattle WA, 417pp.
Hitchcock, C. L. and A. Cronquist. 1973. Flora of the Pacific Northwest. University of Washington Press,
Seattle WA, 730pp.
Pojar, J. and A. MacKinnon. 1994. Plants of Coastal British Columbia. Lone Star Publishing, Vancouver, BC, 527pp.
Raven, P. H., R. F. Evert and S. E. Eichhorn. 1992. Biology of Plants, Fifth Edition. Worth Publishers, New York,
Turner, N. J., L. C. Thompson, M. T. Thompson and A. Z. York. 1990. Thompson Ethnobotany: Knowledge and Usage of
Plants by the Thompson Indians of British Columbia. Royal British Columbia Museum, Victoria, BC, 335pp.
Walters, D. R. and D. J. Keil. 1996. Vascular Plant Taxonomy, Fourth Edition. Kendall/Hunt Publishing, Dubuque,
This page was created by: Tasha Murray, August 2000
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