Giant Horsetail

Giant Horsetail with Fertile Stem © Aschusteff

Equisetum telmateia ssp. braunii

Description (Jepson,

  • Ferns (Polypodiopsida)
    • An early group of vascular plants that produce spores (reproductive cells)
      • Do not produce flowers or seeds
      • Fossil records date back almost 400 million years, versus 130 million years for flowering plants
  • Horsetail Family (Equisetaceae)
  • Perennial herb
    • Grows from rhizomes (horizontal underground stems)
  • Stems
    • Ribbed and hollow, except at joints (nodes)
    • Rough due to tiny grains of silica (sand)
    • Sterile and fertile stems
      • Sterile vegetative stems
        • Green and photosynthetic
        • With whorls of solid, grooved branches
      • Fertile stems
        • Ephemeral, appearing in early spring (shown at right in main photo)
        • Brown (not photosynthetic) and fleshy
        • Cone-like structure (strobilus) of spores at tip
  • Leaves
    • Extremely small, brown, and scale-like
      • Whorled and fused into a freely-toothed sheath, appressed to the stem nodes
    • Usually not photosynthetic
  • Sporangia
    • Spores are produced by sac-like structures called sporangia (singular: sporangium)
    • Found on the inner surface of umbrella-like scales on the terminal, cone-like structures of fertile stems
  • Height to ~2 ft.
    • Fertile stems to ~1.5 ft.
Leaves © SBernhard


  • Native to California
    • Grows along streambanks, roadside ditches, and seeps
    • See Calflora for statewide observations of this plant
  • Outside California, grows in coastal areas of southern Alaska, British Columbia, Washington, and Oregon
  • Grows at elevations to 3,280 ft.

Uses (San Mateo County Parks prohibits removal of any natural material)

  • Native people
    • Young stems were eaten
    • Decoction of the plant used as a diuretic
    • Roots and stems used for basket making
    • Stems used for polishing arrow shafts
      • Abrasive quality comes from silica in the stem epidermis

Name Derivation

  • Equisetum (ek-wi-SEE-tum) – from Latin equus, “horse,” and seta, “bristle,” referring to the stems appearing like the tail of a horse
  • telmateia (tel-ma-TIE-a) – from the Greek telma, “pond” or “pool,” referring to its habitat
  • braunii (BRAWN-ee-eye) – named for Alexander Karl Heinrich Braun (1805-1877), a German botanist who made major contributions to the understanding of basic cell structure


  • Extensive rhizome system allows horsetails (Equisetum species) to rapidly colonize disturbed areas
    • Plants can also regenerate from stem fragments
  • Horsetails (Equisetum species) take up and accumulate silica, protecting the plants from insect and fungal damage (Husby 2002)
  • Spores of horsetails (Equisetum species) have a unique way of travelling by “walking” and “jumping,” aiding in their dispersal (Gill 2013: contains video)
  • Horsetails are often referred to as “living fossils,” as Equisetum is the only remaining genus of the subclass Equisetidae, which for more than 100 million years were a diverse and dominant part of understory vegetation in late Paleozoic forests (Feng 2017)
    • Extinct branching tree ferns, called Calamites, grew to 65 ft. tall
    • Calamites are major components of coal deposits
  • DNA studies have shown that horsetails (Equisetum species) are more closely related to “true ferns” than to the “fern allies” (Lycophytes, e.g. club mosses, spike mosses, and quillworts) in which they were traditional grouped
  • Edgewood’s giant horsetail is classified as a subspecies
    • Subspecies indicates a geographically-separated population with distinct morphological characteristics; when not isolated, interbreeding is possible
    • Variety indicates a population with small morphological variations, e.g. color, seen throughout the geographic range of the species; interbreeding is possible
    • In practice, botanists have not consistently applied these ranks

ID Tips

  • Giant horsetails have distinct features that are unlike other ferns found in Edgewood
    • Erect, hollow, jointed stalks, reminiscent of bamboo
    • Narrow, ribbed green branches, which appear to be whorled leaves
    • Leaves that are non-photosynthetic scales appressed to the stem nodes
    • Fertile stems with spore-producing, terminal cone-like structures

At Edgewood

  • Found in riparian woodland seeps
    • Look for them by the waterfall on the Sylvan trail and in the creek by the Education Center
    • See iNaturalist for observations of this plant

See General References

Special References

Feng, Z. 2017. Late Palaeozoic plants. Current Biology 27: R905-R909. Science Direct.

Gill, V. 2013, Sep. 11. Horsetail plant spores use ‘legs’ to walk and jump. BBC News-Science.

Husby, C. 2003. The giant horsetails. Florida International University.

Pinson, J. 2020-21. About ferns. American Fern Society.

U.S. Forest Service. What are ferns? Forest Service. United States Department of Agriculture.