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Equisetum fluviatile — river horsetail

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Facts

River horsetail is distributed over the northern half of North America, as well as most of the temperate northern hemisphere. It is found in standing water of lakes, streams and marshes. The young shoots are edible, and the mature ones are sometimes used as a scouring tool. In addition, it is an important component of the spring and early summer diet of black bears. It frequently hybridizes with the terrestrial field horsetail where populations of the two species co-occur.

Habitat

Fens (calcium-rich wetlands), lacustrine (in lakes or ponds), marshes, riverine (in rivers or streams), shores of rivers or lakes, swamps, wetland margins (edges of wetlands)

New England distribution

Adapted from BONAP data

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North America distribution

Adapted from BONAP data

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Characteristics

Habitat
wetlands
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island
  • Vermont
Stem form
the stem is relatively straight
Branches
  • there are branches off the main stem, but these branches are not branched
  • there are no branches off the main stem
Cone tip shape
The tip of the spore cone is blunt
Sheathes on older stems
the leaf sheathes persist in older stems
Sheath color
the leaf sheath is mainly black
Stem cross-section
more than half the stem diameter is occupied by the hollow central cavity
Number of stem ridges
9–25
Stem color
the aerial stem color is green
Sheath border color
the border of the leaf sheath is dark, or with a narrow white edge
Length of branch section
the first internode of the branch is shorther than the associated stem sheath
Show all characteristics

  • Leaves

    Leaf length
    2–3 mm
    Leaves per node
    12–24
    Sheath border color
    the border of the leaf sheath is dark, or with a narrow white edge
    Sheath color
    the leaf sheath is mainly black
    Sheathes on older stems
    the leaf sheathes persist in older stems

  • Place

    Habitat
    wetlands
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • New Hampshire
    • Rhode Island
    • Vermont
    Specific habitat
    • edges of wetlands
    • fens (calcium-rich wetlands)
    • in lakes or ponds
    • in rivers or streams
    • marshes
    • shores of rivers or lakes
    • swamps

  • Spores or spore cones

    Cone length
    12–30 mm
    Cone tip shape
    The tip of the spore cone is blunt
    Spore form
    the spores are green and spherical

  • Stem, shoot, branch

    Branch grooves
    the interior of the groove is U-shaped
    Branches
    • there are branches off the main stem, but these branches are not branched
    • there are no branches off the main stem
    How hollow is stem
    75–90
    Length of branch section
    the first internode of the branch is shorther than the associated stem sheath
    Number of stem ridges
    9–25
    Plant height
    350–1150 mm
    Stem cavities
    0
    Stem color
    the aerial stem color is green
    Stem cross-section
    more than half the stem diameter is occupied by the hollow central cavity
    Stem differences
    the vegetative and reproductive stems are similar in appearance
    Stem form
    the stem is relatively straight
    Stem texture
    the stem feels smooth or slightly rough
    Stem thickness
    2.5–9 mm

Wetland status

Occurs only in wetlands. (Wetland indicator code: OBL)

In New England

Distribution

Connecticut
present
Maine
present
Massachusetts
present
New Hampshire
present
Rhode Island
present
Vermont
present

Conservation status

Exact status definitions can vary from state to state. For details, please check with your state.

Massachusetts
unranked (S-rank: SNR)
Rhode Island
extremely rare (S-rank: S1), concern (code: C)

From Flora Novae Angliae dichotomous key

2.  Equisetum fluviatile L. N

river horsetail. Equisetum limosum L. • CT, MA, ME, NH, RI, VT; throughout. Standing water of lakes, streams, and marshes.

1×2. Equisetum arvense × Equisetum fluviatile → Equisetum ×‌litorale Kuhlewein ex Rupr. is a frequent horsetail hybrid known from CT, MA, ME, NH, RI, VT. It occurs mainly on shorelines, in ditches, and in other low areas. It can be identified by its white and misshapen spores (unique for New England Equisetum), monomorphic aerial stems that usually have branches, central cavity 
66–80% of the stem diameter, 7–14 subulate, dark leaves 1–3 mm long, and first internode of branches equal in length to its subtending stem sheath.

Native to North America?

Yes

Sometimes confused with

Equisetum palustre:
nodes with 5-10 leaves per sheath, each leaf with a relatively broad white margin (vs. E. fluviatile, with nodes with 12-24 leaves per sheath, each leaf with a very narrow white margin).

Synonyms

  • Equisetum limosum L.

Family

Equisetaceae

Genus

Equisetum