Named for their resemblance to the wispy bristles of a horse’s tail, these plants belong to a specialized family of ferns called Equisetaceae. Horsetails are considered “living fossils” as their features have largely been conserved through millennia. Fossil records show that today’s modern species likely arose as early as the Jurassic period. Even then, their shoots had already begun to grace the borders of natural water features.
The majority of Equisetum species are native to the Northern Hemisphere, though they are now distributed all across the globe with the exception of Antarctica. These perennials are adapted to a wide range of ambient conditions. In tropical areas, they can be cultivated as evergreen ornamentals for year-round color in the garden. In temperate areas, they tend to die back in winter. Most species spread by rhizomatous growth and may produce dense clonal stands.
Despite the absence of foliage and flowers, horsetails are quite eye-catching and highly structural. Their photosynthetic stems are unmistakable due to their distinct nodes. Their remarkably tiny and non-photosynthetic leaves require close inspection. Moreover, as these plants are types of ferns, they reproduce via spores on strobili. Due to their tolerance for moist conditions, horsetails are regarded as ideal pond edge plants.
1) Marsh horsetail (Equisetum palustre)
The marsh horsetail is considered a wetland marginal plant as it is naturally found along the edges of lakes, pools, streams, marshes, and seeps. It is also found growing in bogs, fens, and sedge meadows in the US. Unlike other horsetail species, it is not known for producing large colonies. In the wild, it is often associated with Juncus, Thuja, and Carex grasses.
E. palustre is often confused with E. pratense and E. arvense due to their similar branch sheath features. It is distinguished by its toothed sheaths, which have about 5 – 10 tiny (3 – 7 mm long) brown teeth a few millimeters above the nodes. This species has two types of stems – a sterile, photosynthetic one and a fertile, blunt-tipped one with a tiny spore cone at its apex. The latter usually matures in summer. A cross-section of these stems shows a circular central cavity surrounded by hollow, polygonal ridges.
The leaf-like branches of E. palustre usually occur at the upper or middle nodes of the shoots. The branches themselves are covered in toothed sheaths. They are usually oriented slightly upward and have a wispy appearance. Mature stems reach a full height of about 80 cm (31 inches). They favor ambient conditions at elevations below 300 m.
2) Water horsetail (Equisetum fluviatile)
Also known as the swamp or river horsetail, the stems of this species are frequently found partly submerged along the margins of streams, ditches, and lakes. They are able to persist in standing or sluggish water up to a depth of about 3 feet (1 m). The moisture-loving root system can thrive in muddy bottoms, where they generate rhizomes to facilitate the plant’s rapid spread. As a result, they have the tendency to become invasive unless they are contained.
This herbaceous perennial typically grows to a mature height of 30 – 100 cm (12 – 40 inches). Its deep green stems are finely ridged. Their lengths are horizontally split into several joints, each covered in a toothed leaf sheath. The whorls of tiny, black-tipped leaves at the upper edge of each joint are about 5 – 10 mm (0.2 – 0.4 inches) tall. Some stems produce whorls of branches at their mid to upper nodes. The longest branches occur close to the middle of the stem, and the shortest ones are borne on the uppermost nodes.
If you cut a water horsetail stem in half, you’ll find that it is almost completely hollow. In fact, its central canal is one of the largest among the horsetail species. Fertile stems are hollow as well but are distinguished from the sterile ones by their spore cones. The young, spring shoots of this species can safely be consumed by many animals. However, large doses can cause toxicity symptoms due to the presence of thiaminase.
3) Scouring rush (Equisetum hyemale)
The scouring rush is perhaps the most popular among Equisetum species for its ornamental uses. In South Africa, it is known as snake grass due to the appearance of its nodes. The stalks are distinctly segmented and are hardly ever branched. They have a remarkably stiff, upright appearance that makes them accentuate the straight borders in modern pond designs. Their tiny leaf sheaths are present as continuous dark bands around each node.
E. hyemale favors habitats that remain consistently moist throughout the year. It favors sandy or gravel-rich substrates where its rhizomes can easily penetrate through the soil. As it can withstand brief periods of flooding, its stems are normally found along the banks of streams and rivers. Mature stems may also be indicative of a nearby water source that has temporarily stopped flowing.
As scouring rush stems tend to reach a maximum height of 3 feet (1 m), they can add vertical interest to water features. Those in marginal locations create vital microhabitats that protect small animals. Apart from their environmental benefits, they have medicinal and domestic uses too. The rough, hollow stems can be used as sandpaper or made into reed instruments.
4) Andean horsetail (Equisetum bogotense)
In its native range, E. bogotense is colloquially referred to as ‘Cola de Caballo’. Traditionally perceived as an herbal remedy, the Andean horsetail can be used to create a highly diuretic tea. The concoction can supposedly increase sodium, chloride, and potassium levels in human urine. As a result, the plant is now used as an ingredient in a few modern-day herbal treatments and supplements.
Like other horsetails, this herbaceous perennial has sheathed, distinctly segmented, stems. Though they are glabrous, their surfaces may be slightly rough due to their silica content. The dark brown to dull green stems are borne on underground rhizomes which can easily spread in moist substrates along the edges of water features.
Due to the isolated distribution of this species, it may be more closely related to fossils or extinct Equisetum species compared to extant ones. Phylogenetically, it appears to be the most distinct horsetail species from the clade in which it is grouped.
5) Meadow horsetail (Equisetum pratense)
One of the most geographically-widespread horsetail species, the meadow or shade horsetail is frequently found in rich forests with generously thick canopies on tall trees. Its preference for moist substrates makes it perfect for growing along the edges of a wildlife or ornamental pond. Its natural stands tend to be thicker when they are closer to sources of water.
E. pratense is distinguished from other similar horsetails by its feather-like and horizontally-oriented branches. Fully parallel to the ground or slightly drooping, these occur in whorls along the nodes of sterile, bright green stems. Hollow stems are horizontally segmented in sheathed joints. At the top rim of each sheath are fine, dark brown teeth with subtly white edges. Unlike the sterile stems, the fertile stems are initially unbranched and are brown to pale pink instead of green.
This species has the capacity to spread into considerably-sized colonies. It has the potential to be a pioneer plant in areas where water stress may have previously opened up large surfaces of land. In areas where it must compete with rich vegetation for space, its shoots may be quite sparse and small.
6) Common horsetail (Equisetum arvense)
Found in all continents apart from Antarctica, E. arvense is a hardy species that can thrive in a variety of climate conditions. In moist areas, its rhizomes can grow downward and penetrate through 6 feet (1.8 m) of substrate! Due to its capacity to become extremely well-established, even chemical means of controlling its spread may be ineffective. Outside of its native range, it is known for being an invasive plant.
The sterile stems of common horsetail grow to an upright maximum height of about 90 cm (35 inches). It is horizontally split into joints with internodes that are about 2 – 5 cm (0.8 – 2 inches) long. Branches, which may often be referred to as side shoots, arise along whorls on each segment. There may be as many as 20 branches per whorl. Their proliferation gives the plant a crowded and highly textural appearance. In contrast, fertile stems reach a maximum height of about 25 cm (10 inches) and are usually off-white instead of bright green.
This species has many medicinal uses due to its rich nutrient profile. Its buds are edible as vegetables, though a large amount is considered toxic. If you intend to cultivate the common horsetail around your pond or in your garden, make sure to restrict its spread to within a pot or container.
7) Wood horsetail (Equisetum sylvaticum)
If you’re after a horsetail pond plant with a more elegant appearance, consider planting E. sylvaticum. The stems of this lovely species look as though they have delicate and gently arching skirts along each joint. The drooping branches, which occur in the signature horsetail whorls, are themselves branched. They give the plant a spritely and complex appearance.
The segmented stems of the wood horsetail grow to a full length of about 60 cm (24 inches). Their leaf sheaths are slightly different from those of other horsetails in that they are more inflated along the base and tighter around the stem just under the toothed upper edge. On fertile stems, which tend to be much shorter compared to sterile ones, the leaf sheaths tend to be looser.
This species produces remarkably long-lived and deep rhizomes in optimal substrates. Oftentimes, the volume of growth underground is tens of times that of the above-ground features. Dense colonies are usually indicative of cool climates and permanently moist, slightly acidic soils in healthy forests.
8) Great horsetail (Equisetum telmateia)
The great horsetail comes in two main subspecies; E. telmateia subsp. telmateia and E. telmateia subsp. braunii. The latter, which has a natural distribution restricted to North America, has evenly green features along the length of its stem. The former has whitish-green joints in between the whorled branches. The fertile stems of both subspecies tend to have a more yellowish hue.
The joints of the great horsetail are increasingly heavily-branched closer to the tip of the stem. Each whorl may have as many as 40 branches. Towards the base, the lowermost segments remain unbranched. Sterile stems typically reach a maximum height of 150 cm (5 feet), making this plant one of the tallest horsetail species. In early spring, the fertile stems begin to appear before the sterile ones do. They are much shorter and possess no side branches. Once the spores are released, the fertile stems quickly die back.
In the wild, the giant horsetail is typically found in shady areas with consistently damp substrates. It can also form considerably large colonies in woodlands, fens, and along strips of land that accumulate seepage.
9) Smooth horsetail (Equisetum laevigatum)
E. laevigatum is quite similar to E. hyemale and E. variegatum. The features that distinguish it from the latter two species are largely dependent on the stage of shoot growth. Young stems have leaf sheaths that are edged with distinctly black teeth. Over time, the teeth dry off completely and begin to drop off. They leave a neat, dark-colored ring that encircles the top part of the sheath.
Fertile stems are closely similar to sterile ones, but they are easily spotted due to the presence of their pointed spore cones. Segmented branches, which look like miniature versions of the stems, may occur along the mid to upper nodes. Mature plants grow to a maximum height of up to 120 cm (4 feet). They are known for having a fast growth rate, particularly in clay or loamy soils with moderate to high moisture levels.
10) Dwarf horsetail (Equisetum scirpoides)
If you’re in need of smaller horsetails, the dwarf horsetail may be the perfect edge plant for your pond. Its unbranched stems tend to grow to a maximum height of just 25 cm (10 inches). Don’t be fooled by their relatively diminutive size, however, as they can quickly spread to cover an indefinite area.
Unlike the firm and upright stems of most horsetails, those of E. scirpoides may appear wiry and mangled. Despite their short lengths, they can twist and become tangled with one another when blown by strong gusts of wind. Both sterile and fertile stems are markedly segmented, with each joint covered by a bright green leaf sheath.
Versatile and highly adaptable, this species can dominate regularly moistened substrates in tundras and coniferous forests. Evergreen, dwarf horsetail stems are able to tolerate being partly submerged in up to 5 cm (2 inches) of water. This makes them ideal marginal plants for sloping edges.
11) Variegated horsetail (Equisetum variegatum)
E. variegatum is a highly variable species with a morphology that tends to differ depending on the specific environmental conditions of the geographic location. As a result, it comes in several varieties. Some of these have the tendency to creep above the substrate, whereas others maintain a fully upright position along the edges of lakes, canals, and streams.
Both fertile and sterile stems are unbranched and covered in leaf sheaths. If you look closely at the dark band along the upper edges, you’ll find that each tooth is bordered on both sides with white edges. The teeth are able to persist through the seasons on the evergreen stems. If you take a cross-section of the plant, you’ll find that the central cavity exposes a smaller section of the stem compared to the hollows of other species.
12) Mexican giant horsetail (Equisetum myriochaetum)
The tallest of all extant horsetail species, E. myriochaetum can become as tall as a tree! Some of the tallest individuals have grown to more than 20 feet (6 meters) tall. As their features are simply the oversized versions of branched horsetails, dense stands may form a highly bristled canopy. Interestingly, although the stems of this Mexican giant grow much taller than those of North America’s giant horsetail (E. giganteum), their maximum diameter (1.8 cm) is not nearly as large.
E. myriochaetum produces fertile stems, but it chiefly spreads to form its colonies via rhizomatous growth. In the wild, it favors regularly moistened or wet areas with fertile soil. It is a tropical to subtropical species with a preference for ambient temperatures ranging from 15 – 20˚C (59 – 68˚F). Frost is unfortunately not tolerated, so it would be best to avoid growing this plant around ponds in northern temperate zones.
