Horsetails are allies of ferns. These are ancient plants with distant relatives back in the Carboniferous period. The Water Horsetail is quite common in swamps and wet areas. It lack flowers and regular leaves and produces spores instead of fruits.
The thick stem is dark green, 80% hollow, jointed, with a membrane, or sheath, at each joint. The stem has 10 to 30 fine ridges which continue through the node and through the sheath, ending with 12 to 20 dark brown tooth-like points, or scales, at the top of the sheath. These points are sometime fringed in white. Stems reach 2 to 3 feet in height. These membranes or sheaths, are square-ish looking in face view (as tall as wide). From the base of the sheath along the mid-stem section, emerge the thin branches, forming a whorl, and on the branches are the plants version of leaves. Some stems may branch near the top.
Leaves: These thin branches of the stem have 1 to 8 nodes with a whorl of 5 scales (the true leaves) per node.
Spore production: Fertile stems end in a small spore producing cone known as a Strobilus. These mature in mid-summer. Non-fertile stems look the same except lack the cone. Because of the narrow stem walls, the stem is easily collapsed.
Propagation and habitat: The plant grows and usually spreads from a rhizome in moist soils to shallow waters less than 40 inches deep. It can be quite aggressive to invasive, creating dense colonies. The spores can also produce new plants. The spore producing organs are housed around the strobilus cone in whorls of shield shaped structures called sporophylls, each of which contains 5 to 10 organs called sporangia producing the spores.
Names: The genus name, Equisetum, is Latin for "horsetail" and the species name, fluviatile, refers to a river. The author name for the plant classification, 'L.', refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: Water Horsetail has male and female stems that look alike and is similar to the Marsh Horsetail, E. palustre, but that species has only 5 to 10 stem ridges, fewer than 11 sheath teeth which are usually fringed in white, and the sheath itself is elongate in face view (see drawing comparison below). Compare also Field Horsetail, E. arvense, when the fertile stems look entirely different from the sterile stems.
Above: Stems and tips of Water Horsetail. There is extensive growth of the plant in the wetland area of the Garden.
Below: 1st & 2nd photos - The dark points are the termination of the stem ridges and project from a membrane that is as high as it is wide. On the young stem you see the beginning growth of the ascending branches, which will have small scale leaves at the nodes. 3rd photo - The hollow stem.
Below: 1st photo - A fertile stem with the strobilus on top and whorls of branches emerging from the sheath-like membrane. 2nd photo - The strobilus is the spore producing organ that appears on top of fertile stems. The spores are produced in a sporangia, similar to a fern. The sporangia are contained in the small shield-like structures that form whorls around the strobilus.
Below: A comparison drawing of Water Horsetail (#s 4 & 5) and Marsh Horsetail (#3). Drawing ©Flora of North America.
Notes: Eloise Butler did not note Water Horsetail in her inventory of indigenous plants in 1907, but instead listed 4 other Equisetum species as present in a 1919 article she wrote for the Agassiz Association. Martha Crone does not list the Equisetaceae family on her 1951 Garden Census, but nevertheless, it is so prevalent in the wetland area today that it may certainly have been established at that earlier time. She wrote about it in the October 1953 issue of The Fringed Gentian™, saying it is "the last remainder of the large trees of the carbon forests, propagating by spores and creeping rootstalks." See it on the wetland path - Lady Slipper Lane. It is native to most of Minnesota except the drier parts of the SW quarter. The plant is on the endangered list in several New England States. It occurs in North America northward of a line from Oregon to Virginia.
There are 13 different species of Equisetum found in Minnesota 9 of which are found in Hennepin County.
Lore and uses: The stems of Horsetails contain much silica and have been used historically in the new and old world for scouring and sanding, although the method by which Horsetails accumulate this silica is mostly unknown. [for technical details see this abstract] There is also some reference for folk medicinal use, principally as a diuretic. Environmentally, they absorb heavy metals form the soil and are therefore quite useful in degraded sites.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"