Equisetum arvense L.
Common horsetail, field horsetail, prêle des champs.
Equisetaceae, horsetail family.
Sp. Pl. 2: 1061. 1753.
Type: Hauke (1963) studied the typification of E. arvense and designated LINN packet number 1241 and sheet number 4 as the type.
Equisetum arvense var. alpestre Wahlenb.
Equisetum arvense var. boreale (Bong.) Rupr.
Equisetum arvense var. riparium Farw.
Equisetum arvense var. calderi Boivin
Plants perennial herbs; dimorphic aerial stems persisting for one year or less: vegetative stems green, with branches at stem nodes in whorls of 3–4; fertile stems, pallid brown, unbranched, shorter than the vegetative stems, with larger sheaths; fleshy; short-lived; with perennial underground black stems, (see image library); less than 15 cm high (cold habitats), or more than 15 cm high; 2–40(–100) cm high. Roots pallid-brown, or red-brown, or black. Ground-level or under-ground stems horizontal; rhizomatous (usually); elongate, or compact; 0.7–2 mm wide. Scales present; 3–4; (0.5–)2–5(–10) mm long ((0.5-) 2–5(-9) mm wide); glabrous. Aerial stems erect; conspicuously jointed with nodes covered by whorls of tiny leaves fused for part of their length into sheaths that are tipped with teeth (branches develop in regular 3–4 channels between the ridges; the first internode of each branch is longer than the subtending stem sheath); not filiform (usually); squarish; with 3–4 ridges; glabrous (the nodes covered by leaf sheaths or branches). Branches yellowish (usually present; absent in other Canadian Arctic Equisetum taxa). Leaves distributed along the stems; whorled; simple; deciduous (on stems that persist for 1 year or less). Petioles absent. Leaf bases truncate (into the fused sheath). Blades 0.5–1 mm long (these are the "leaf teeth" of Flora North America, vegetative stem leaves; 0.1–0.3 mm long); 0.05–3 mm wide (leaves on the fertile stems with larger, fleshy, sheaths); appressed to the stem; herbaceous (or scarious); straight; lanceolate, or triangular; flat; with parallel veins, or appearing single-veined, or with inconspicuous veins; adaxial surface glabrous. Blades abaxial surface glabrous. Leaf apices acuminate, or acute. Plants asexual, or reproducing by spores borne in sporangia. Sporangia in terminal cone-like structures (on pale brown fertile stems that lack chlorophyll; cones mature early in the spring.).
Chromosome information. 2n = 216 (approximately).
Distribution. Circumpolar. Arctic. Range in the Canadian Arctic Archipelago widespread. Greenland, St. Pierre and Miquelon, Canada, United States, Eurasia. USA: Alaska. Arctic Islands: Baffin, Ellesmere, Axel Heiberg, Banks, Victoria, Somerset, Southampton.
Ecology and habitat. Elevation 0–400 m. Substrates, wet meadows, along streams, lake shores, tundra, ridges, cliffs; imperfectly drained moist areas, on seepage slopes, on solifluction slopes, moderately well drained; calcareous; gravel, silt, clay, till, moss; with low organic content. Hauke (1963) found that E. arvense occurs on a wide variety of substrates, clay, gravel, sand, crushed stone and rich loam. Often plants appeared to be growing in dry areas but these were usually obviously associated with ground water supplies, in sites such as roadside fill above swampy places. He hypothesized that E. arvense is dependent on an abundant water supply and documented digging down into a recently filled area adjoining a swamp to discover that the Equisetum stems had come up through over three feet of sand, and that there was a horizontal rhizome system in the saturated swamp soil underlying the fill. Hauke (1963) also noted that the more open and harsh the habitat, the more depauperate and aborted the plants, indicating that external conditions, such as summer frosts, can change normal development. This is documented for the Arctic in the image library where there is a picture of a herbarium specimen in which the plant is less than 3 cm tall with almost no stem branches. Underground, it appears to have been growing as a sand binder in an exposed site at nearly 81°N. A second image shows a much branching plant 20 cm high, that was growing in the shelter of rocks, at a site more than 81°N.
Notes. Field horsetail is well known to be a poisonous plant. Hay containing this weed is apparently more dangerous than pastures with horsetail. The deaths of many horses have been reported to veterinarians, but there is reason to believe that many more losses are unreported Frankton and Mulligan (1987).
Among the many infraspecific taxa that have been named in this species, Equisetum arvense var. boreale Bongrad has been most generally accepted and has been applied to plants with tall, erect stems with 3-ridged branches. Because both 3-ridged and 4-ridged branches may occur on a single stem the variety boreale is not recognised in the Flora of North America treatment, Hauke (1993). In the developing PanArctic Flora checklist Equisetum arvense var. alpestre Wahlenb. and Equisetum arvense var. boreale (Bong.) Rupr. are synonymous under the name Equisetum arvense var. boreale (Bong.) Löve.
Hauke (1963) in a systematic study of E. arvense indicated that it is the most common and widespread species of the genus Equisetum. Its odd morphology has attracted much attention, and resulted in a remarkable number of infraspecific taxa being described. The most extreme author being Gandoger (1891) who recognised 62 forms. Hauke (1963) did a detailed study involving herbarium specimens, field work, and transplant studies. He found that the contined production of new stems is one source of variation within a single clone of E. arvense. Stems when young may have short, simple branches (forma varium Milde), but when mature the branches are long, frequently becoming rebranched (forma pseudo-sylvaticum Milde) and may develop dark teeth (forma nigricans Warmst). Also stems produced when the surrounding vegetation is undeveloped may be low and spreading (forma decumbens Meyer). In exposed places, decumbent or prostrate plants, or even plants with the main stem aborted and several compound branches arising from the underground portion of the stem, may give the appearance of thin stems.
Raup (1949) illustrated the effect of shifting sand in an Indiana dune on E. arvense where it produced forms alpestre Wahl., diffusum A.A. Eat., ex Gilbert, and decumbens Meyer, all on the same rhizome. These observations were mostly made south of the 49th parallel, and apply even more in the Arctic.
Schaffner (1929) showed variation on a single plant with respect to branch number and commented that if one would base the validity of the variety boreale (Bong.) Rupr. on the character of its branches, one would have to pull plants to pieces and name the dissected parts separately. Kato (1964) presented a graph showing that, at least in Japan, the lowermost nodes of a plant bore mostly 4-angled branches, the uppermost mostly 3-angled. It was suggested that the difference in the number of angles is related to whether the plant is growing in sun or shade. Hauke (1963) suggested that this apparent correlation breaks down when one gets into the Arctic and the shade form disappears, but does it? The image library has a picture of a plant that was growing between rocks at 81°N and possibly quite shaded.
One obvious feature of E. arvense is the dimorphism between its vegetative and fertile stems. All conditions exist, from fertile stems producing a few branches (var. irriguum), to fertile stems like the sterile stems. The later forms are frequent northward, where they are often depauperate (E. calderi Boivin).
The physiology of fruiting is not understood. Whatever it is, there is a control mechanism that can be upset. Depending upon when and how it is disrupted a fertile stem may develop branches which is not surprising since the dormant branch apices are present. Conversely, a vegetative stem may develop a cone, which is less easily explained since the shoot apical cell must change its pattern of activity. Occasionally an apex begins to produce a cone then reverts to vegetative activity, and a proliferated cone is produced. (Illustrated Hauke 1963).
Hauke (1963) concluded that E. arvense is a noteworthy plant in the many different growth forms it can assume, but evidently these are only superficial modifications and none deserves taxonomic recognition. The reliable characters that characterise this species are: rhizomes, including the internodes felted, branches 3–4 angled, with the first branch internode longer than the subadjacent teeth, stem sheaths slightly longer than they are wide, slightly involute or appressed to the stem, and branch teeth with subulate tips. These, and some internal anatomy characters, differentiate this species from all other taxa and remain essentially constant in spite of various gross plant modifications.
Illustrations. • Plants in muddy habitat. Pale orange-pinkish, fertile plants between the markers and common in the environment with Polygonium viviparum. Wet muddy banks of a side stream beside the Thomsen River, Banks Island, Aulavik National Park, 8 July, 1999. Susan Aiken 99–025. CAN. • Close-up of plants. Pale orange fertile plants that lack chlorophyll, growing with Polygonium viviparum in wet muddy banks of a side stream beside the Thomsen River, Banks Island, Aulavik National Park, 8 July, 1999. Susan Aiken 99–025. CAN. Scale bar in cm. • Close-up of young cone. Fertile cone, about 1 cm long, that has opened to expose pale yellow sporangia that hang from underneath of the flattened brown surface of each unit of the cone. Thomsen River, Banks Island, Aulavik National Park, 8 July, 1999. Susan Aiken 99–025.CAN. • Sterile and fertile stems. Left, a green, vegetative stem that is branching at the nodes. Right, a paler, fertile stem with no branching at the lower nodes, and only the beginnings of branching higher up. Note that the leaves on the fertile stem are larger and more flesy than those on the sterile stem. Specimen collected Nunavut, Baffin Island, Arctic Bay. 12 Aug. 1927, CAN 3173. • Vegetative stem branching. Plant separated from associated moss to show ground-level and above ground branching and jointed stems. Note that the first internode of each branch is longer than the subtending node. Nunavut, Ellesmere Island, near John Richardson Bay 80°21'N, 71°21'W. S.G. Aiken 98–042. Photograph by Mollie MacCormac. • Plants in mossy habitat. Wiry, high arctic plants that were growing on a wet seepage slope, Sample removed to adjacent drier ground for the photograph. Nunavut, Ellesmere Island, Scoresby Bay 79°53'N, 71°33'W. S.G. Aiken 98–018. Photograph by Mollie MacCormac. • Close-up of older stems and leaves. Close-up to show jointed stems that are marked by a brown ring and white scale-like, old leaves overlapping the node. Plants growing on Ellesmere Island, Nunavut, at Scoresby Bay 79°53'N, 71°33'W. S.G. Aiken 98–018. Photograph by Mollie MacCormac. • Plant root. Plant with long and healthy root. Plant was teased out of deep moss, in very moist habitat. Nunavut, Ellesmere Island, near John Richardson Bay 80°21'N, 71°21'W. S.G. Aiken 98–042. Photograph by Mollie MacCormac. • Close-up of stunted plant. Brown, wiry, branching, underground stems that have probably been growing as a sand binder in a flood plain habitat near the outflow of a river. Fertile stems without chlorophyll confirm the identification. Note their large leaves. Above ground vegetative stems less are than 3 cm tall, with narrow, E. scirpoides-like stems. Below ground stems at least five times the length of aerial stems. Collection from Ellesmere Island, Borup Fiord. just below 81°N CAN 556099. • Close-up of plants 25–30 cm tall. Herbarium specimens of plants collected further north than previous image and looking more like southern E. arvennse. Collected on Ellesemere Island, Head of Tanquary Fiord, just above 81°N, growing in the shelter or rocks. CAN 320182. • Close-up of plants in habitat. Plants similar to those found in southern fields, growing on the beach. Note whorls of branches arising along the jointed stems. N.W.T., Tuktoyaktuk, beach area, J.M. Gillett 18717. CAN. • Type herbarium specimen. Type specimen of Equisetum arvense var. alpestre Wbg. N.f. circulare Nunavut, Alex Heiberg Island A.H.I., Hugh Thomson Valley, 1 Km W of Hugh Thompson glacier, 10msm, on silt flat, S.shore of river, prostrate, circular growth. R. Beschel 11167, 28 July, 1960, CAN. Scale bar in cm. • Arctic Island Distribution.
Cite this publication as: S.G. Aiken, M.C. LeBlanc, and M.J. Dallwitz 2000 onwards. Pteridophytes of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval.’ Version: 23rd February 2001. http://www.mun.ca/biology/delta/arcticf/’. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993, 1995, 2000) , and Aiken, Dallwitz et al. (1999) should also be cited (see References).
