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Equisetum


 
KingdomPlantaePlants, but not fungi, lichens, or algae
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
GenusEquisetumFrom equus, horse; and seta, bristle

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 plants’ unusually high levels of silica. They are often classified with ferns, but they are a distinct group of vascular plants. Like ferns, they reproduce by spores, not seeds. 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, and were dominant species during the late Paleozoic Era. All horsetails prefer damp to wet freshwater soils.

For excellent comparison photos, see APHOTOFLORA. And this Equisetum comparison key. And the chart below.

 

Equisetum

Field horsetail (Equisetum arvense) · 9/18/2016 · Shore Acres Preserve

Equisetum

Common scouring rush (Equisetum hyemale) · The sheaths are black at both the bottom and top. · 12/12/2020 · Mitchell Field, Harpswell, Maine

 
Equisetum arvense

Equisetum fluviatile

Equisetum hyemale
Common Name

field horsetail

water horsetail

rough horsetail
Leaves

 

Tiny, dark brown sharp-tipped leaves surround the stem at nodes. Photo by Enrico Blasutto.

 

Each stem node is wrapped with tiny, black, sharp-tipped scale leaves. Branch nodes also have miniscule leaves that appear as black dots. The leaves do not perform photosynthesis; this is done by the stem and branches. Cropped from a photo by Luc Viatour.

 

Each stem is punctuated by nodes surrounded by sheaths. The sheaths are actually tiny leaves, fused to the stem.
Stem Fertile stems, tipped by conelike structures, are pale brown, erect, and unbranched. They are 6-12" (15-30 cm) tall. They appear early in the season and are gone by May. Sterile stems are green, 6-24" (15-60 cm) tall, ¹/₁₆-³/₁₆" (3-5 mm) in diameter, with 4-14 ridges. They appear after the fertile stems have come and gone. They are highly variable, usually heavily branched in a series of upward-pointing whorls, usually erect, sometimes prostrate. Branches are thin, shaped like a plus sign in cross-section. Stem and branch surfaces feel rough. In dense colonies, unbranched or multiply branched. Fertile and sterile stems look the same. 14-46" (35-116 cm) tall, with dark green stems ¹/₁₆-¼" (2-8 mm) in diameter. If branches are present, they are less than 3" (7.6 cm) long, with 8 or fewer nodes. Each segment boundary is ringed by a series of tiny, black-tipped scale leaves. The stems of water horsetails are entirely hollow, and smoother than marsh horsetails. The stems pull apart easily at the joints.

 

Typically a single, rough-textured unbranched, dark green stem, 7-86" (17-218 cm) tall. Rarely has a few branches that tend to be nearly attached to the vertical stem.
Fruit

 

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

 

The spore-bearing, conelike strobili are yellow-green, ⅜-¾" (1-2 cm) long. Photo by joelpk@flickr.

 

Conelike structures at stem tips, strobili, are ½-1" (1.3-2.5 cm), with sharp tips. This one is immature.
Range/ Zones

USDA Zones: 4-9
Habitats Fields, woods, marshes, roadsides, especially damp areas in partial shade Ponds, marshes, slow-moving water  
Type Wild Wild Wild
Occurrence   Common, sometimes considered invasive  

 

 
Equisetum palustre

Equisetum pratense

Equisetum scirpoides
Common Name

marsh horsetail

meadow horsetail

dwarf scouring-rush
Leaves Sheaths appearing at nodes along the stem contain 8-10 tiny, non-photosynthetic leaves, shaped like sharp dark spears. Tiny, non-photosynthetic leaves called scales are fused to the stem at branch nodes, or sheaths. Sheaths are ¹/₁₆-⅛" (2-6 mm) long, with 8-10 brown, white-edged teeth. Non-photosynthetic leaves are in thin sheaths of three (rarely four), black or dark brown in color, wrapped around the narrow stems. The sheaths have a white edge.
Stem Plants are evergreen, rough-textured, 4-20" (10-50 cm) tall. They have 4-12 (usually 8-10) ribs, and are ¹/₃₂-⅛" (1-3 mm) around. In cross section, stems show vallecular canals about the same size as a central hollow region. The central hollow is much less than half the diameter of the stem. Fertile and sterile stems look similar, except for a cone at the tip of the fertile stems, vs. a stem that tapers to a point in sterile stems. The first sheath on the branch (aka first internode) has 5 or 6 narrow teeth, and the first branch internode is shorter than the stem sheath. Fertile and sterile stems also emerge at about the same time. Thin light green fragile-looking branches, in symmetric whorls, <24" (60 cm) in height. Branches tend to be straight, or to droop somewhat, while in other species the branches are ascending. Stems are ¹/₃₂-⅛" (1-4 mm) in diameter, with 8-18 ridges. In cross-section, up to half the diameter of the stem is hollow, more than marsh horsetail. Fertile stems are 8-10" (20-25 cm) tall, and pale pink or brownish at first, tipped by a cone-like structure. After fruiting, fertile stems become green and develop branches, looking like the sterile stems. Sterile stems are 8-24" (20-60 cm) tall, and very rough. The smallest horsetails, often occurring in low, twisted, tangled-looking mats, intertwined with mosses and grasses. 1-8" (2.5-20 cm) tall. Stems are unbranched, but thin enough to look like branches of other horsetails. Fertile and sterile stems are evergreen, with six broad ridges. They occur together and look almost identical, except that the fertile stems are a bit more erect, and tipped by a small black conelike structure; while the sterile stems are more curved and unstructured. Stems have a central hollow less than a third of the diameter, smaller than most horsetails.
Fruit A conelike structure about ¾-1" (2-3 cm) long, the strobilus, appears at the tip of each fertile stem. Fertile stems are tipped by a single blunt-tipped cone-like strobilus, ½-1½" (1.5-4 cm) long, atop a stalk. Spores are released in April. Fruits are a narrow conelike structure called a strobilus, appearing at the tip of each fertile stem. Each “cone” is ¹/₁₆-⅛" (2-5 mm) long.
Range/ Zones

USDA Zones: 1-9
Type Wild Wild Wild

 

 
Equisetum variegatum
Common Name

variegated horsetail
Leaves Tiny, non-photosynthetic leaves form small sheaths that encircle nodes along the stem. There are 3-14 tiny, sharp-pointed black leaves, often called teeth, per sheath. Each sharp black tooth is surrounded by white. The teeth tend to persist all season, and they are sometimes tipped with hairlike bristles.
Stem Usually stems are erect, though they may bend under their weight. Sterile stems are evergreen, rough, 3-19" (7.6-48 cm) tall, ¹/₃₂-⅛" (1.5-4 mm) in diameter, dark green and unbranched. They have 3-12 vertical ridges. In cross section, the stems have a central cavity that is ¼ to ⅓ of the diameter of the stem. Vallecular canals, which ring the central cavity, are a bit less than half the diameter of the central cavity. Fertile stems resemble the sterile stems, but there is a “cone” atop each stem.
Fruit A “cone”—strobilus—appears at the tip of each fertile stem. It is green, with a black, sharp-pointed tip, and ⅛-¼" (5-8 mm) long. The spores are green, and spherical.
Type Wild

 

Online References:

Equisetum on Wikipedia

Equisetum on www.aphotoflora.com

Equisetum on michiganflora.net

References:

Cobb, Boughton, Farnsworth, Elizabeth & Lowe, Cheryl, Peterson Field Guides: A Field Guide to Ferns and Their Related Families of Northwestern and Central North America, Houghton Mifflin Company, 2005, p. 333

Equisetum

Common scouring rush (Equisetum hyemale) · 9/3/2020 · Mitchell Field, Harpswell, Maine
≈ 6 × 10" (16 × 24 cm)

 

Equisetum description by Thomas H. Kent, last updated 1 Dec 2020.

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Equisetum

Rough horsetail (Equisetum hyemale) · 9/4/2013 · Amos Kendall Conservation Area, Dunstable, Mass­a­chu­setts
≈ 3 × 3" (8 × 7.6 cm) ID is uncertain

Equisetum

Meadow horsetail (Equisetum pratense) · About 8 x 5" · 9/4/2010 · Old Rail Trail near Wilkins Farm, Pepperell, Mass­a­chu­setts ID is uncertain