Flora of the Canadian Arctic Archipelago

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S.G. Aiken, M.J. Dallwitz, L.L. Consaul, C.L. McJannet, R.L. Boles, G.W. Argus, J.M. Gillett, P.J. Scott, R. Elven, M.C. LeBlanc, L.J. Gillespie, A.K. Brysting, H. Solstad, and J.G. Harris

Equisetum arvense L.

English: Common horsetail, field horsetail, goosefood,

French: Prêle des champs.

Equisetaceae, Horsetail or Scouring rush family.

Published in Sp. Pl.: 1061. 1753.

Type: Clayton 341, selected by Jonsell and Jarvis, Nordic J. Bot. 14: 148. 1994. Lectotype: BM.

Synonymy. Equisetum arvense L. var. alpestre Wahlenb. Fl. Lapp. 296. 1812.

Equisetum boreale auct. non Bong., Mém. Acad. Imp. Sci. St.-Petersb., Sér. 6, 2: 174. 1832.

Equisetum arvense L. var. boreale auct. non (Bong.) Rupr., Beitr. Pflanzenk. Russ. Reich. 4: 91. 1845.

E. arvense subsp. boreale auct. non (Bong.) A. Löve, Náttúrufrædingurinn 18: 101: 1948.

E. arvense fo. decumbens (G. Mey. ) W.D.J. Koch. Syn. Fl. Germ. Helv., ed. 2. 964. 1845.

Vegetative morphology. Plants 1–40(–100) cm high; herbs; perennial herbs; not caespitose; never vegetatively proliferating by bulbils on stems or leaves, in inflorescences, from gemmiphores and gemmae, or by fragmentation; jointed fertile stems without pigmentation, or with pigmentation (often lower nodes may remain green and branching). Only fibrous roots present. Roots pallid-brown, or red-brown, or black. Ground level or underground stems horizontal, or vertical; rhizomatous; elongate; 0.6–2 mm wide. Ground level or underground stems scales present; 3–4; dull brown; (1–)2–3 mm long; glabrous. Caudex absent. Aerial stems developed; erect, or ascending, or prostrate; not conspicuously jointed. Aerial stem ridges 3–4; the same number as that of the leaf teeth at each node. Leaves absent or leaf teeth; leaf teeth (in whorls distributed along the stem). Leaf teeth persistence annual, dying at the end of the first season. Leaf teeth 0.1–1 mm. Leaf teeth 0.05–3 mm (leaves on the fertile stems with larger, fleshy, sheaths). Leaf teeth dull with pale centres and dark brown margins.

Reproductive morphology. Plants with sporangia, or vegetative leaves without obvious spore-bearing organs. Sporangia in terminal cone-like structures (cones mature early in the spring). Aerial stems squarish in cross-section.

Chromosome information. 2n = 216.

2n = more than 200, Packer and McPherson (1974, northern Alaska), as E. arvense, probably this subspecies, listed as subsp. arvense and 'corrected' to 2n = about 216 by Löve and Löve (1975).

2n = 216 (2x). Löve and Löve (1961c, Iceland).

2n = 216. Löve in Bir (1960, Iceland); Löve and Löve (1961c, Iceland); Löve (1976); Hauke (1993, Fl. N. Amer. 2, secondary reference) as well as some more southern counts.

Indigenous knowledge. Andre and Fehr (2000) noted that Gwich'in people know that this plant is eaten as food by geese and muskrats. The root tubercles can be eaten raw, and the leaves and stems can be steamed for nasal congestion, colds, and stomach ailments. The coarse green stems may be gathered and used to scrub pots and clean dishes.

Ecology and habitat. Elevation 0–400 m. Substrates: wet meadows, along streams, lakeshores, tundra, ridges, cliffs; imperfectly drained moist areas, seepage slopes, solifluction slopes, moderately well-drained areas; gravel, silt, clay, till, moss; with low organic content; calcareous. 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 hypothesised 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 3 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.

Mossy carpets along the shore of a small kettle lake (CAN 296319); wet muddy soil of lake (CAN 502890); plants growing in moss on small "islands" in a hanging fen (CAN 581941).

North American distribution. Alaska, Yukon, Northwest Territories Islands, continental Northwest Territories, Nunavut Islands, continental Nunavut, northern Quebec, Labrador. Range in the Canadian Arctic Archipelago widespread. Uncommon, rare. High Arctic. Arctic islands: Baffin, Ellesmere, Axel Heiberg, Parry islands (Melville), Banks, Victoria, Somerset, Southampton.

Northern hemisphere distribution. Circumpolar, or circumboreal. Northern Iceland, Northern Fennoscandian, Kanin–Pechora, Svalbard – Franz Joseph Land, Polar Ural – Novaya Zemlya, Yamal–Gydan, Taimyr – Severnaya Zemlya, Anabar–Olenyok, Kharaulakh, Yana–Kolyma, West Chukotka, Wrangel Island, South Chukotka, East Chukotka, West Alaska, North Alaska – Yukon, Central Canada, Labrador – Hudson Bay, Ellesmere Land – Peary Land, West Greenland, East Greenland.

General notes. Equisetum arvense is the most common and widespread species of the genus Equisetum (Hauke 1966). Its odd morphology has attracted much attention, and resulted in a remarkable number of infraspecific taxa being described. The most extreme treatment has been by Gandoger (1891) who recognised 62 forms.

These extreme treatments are, in part, due to variation within clones. Hauke (1963) found that, as new stems are continually produced, young stems may have short, simple branches (forma varium Milde), but mature branches are long, frequently becoming branched (forma pseudo-sylvaticum Milde) and may develop dark teeth (forma nigricans Warnst). Also, stems produced when the surrounding vegetation is undeveloped may be low and spreading (forma decumbens Meyer). Rapp (1949) illustrated the effect of shifting sand in an Indiana dune on E. arvense s.l. where it produced forms alpestre Wahlenb., diffusum A.A. Eaton ex Gilbert, and decumbens Meyer, all on the same rhizome. Schaffner (1928) showed variation on a single plant with respect to branch number. 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 was 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 resembling the sterile stems. The latter forms are frequent northward, where they are often depauperate (E. calderi B. Boivin).

Hauke (1966) 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 as follows: 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 characters, plus some internal anatomy characters, differentiate this species from all other taxa and remain essentially constant in spite of various gross plant modifications.

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 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 in Hauke 1963).

Elven et al. (2005) state that "there have been many doubts about whether there is a separate arctic-alpine race or only a group of arctic modifications. A race was reluctantly accepted by Øllgaard in Jonsell (2000). Both Tzvelev and Elven tend to accept it as a subspecies, but Elven commented that its reported distribution in European Russia and Siberia seems very large compared with its strict restriction to northern high alpine and clearly arctic areas in northwestern Europe and North America. Schönswetter et al. (2001) argued for acceptance as a separate race, based on several morphological criteria." Hauke (1993, Flora of North America treatment, p. 81) states, ‘Among the many infraspecific taxa that have been named in this species [E. arvense s.l.], E. arvense var. boreale (Bong.) Á. Löve, 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 here as distinct.’ Schönswetter et al. (2001) convincingly argued that the name 'borealis', more or less uniformly applied for this arctic-alpine race, has been misapplied. It is based on plants from Sitka in southeastern Alaska that differ from the arctic and high alpine plants in most morphological features. The next available name is Wahlenberg's var. alpestre.

Much of the material in the Flora region aligns with E. arvense var. alpestre, but further study is required on the North American specimens. Therefore, following Hauke (1993), here we treat this taxon as a species in the broad sense.

Field horsetail is well known to be a poisonous plant. Hay containing this weed is apparently more dangerous than the plants are when they are growing in pastures. The deaths of many horses, particularly young horses, have been reported to veterinarians, but there is reason to believe that many more losses are unreported (Frankton and Mulligan 1987).

Illustrations. • Habitat: Baffin Island, Iqaluit. Vigorous colony in low lying area. Both fertile and vegetative stems present. Vegetative shoots growing prostrate in sandy ground in foreground and growing erect behind. Nunavut, Baffin Island, Iqaluit. Aiken and LeBlanc 04–021. CAN 586494. • Habitat: Sachs Harbour. Abundant bright green plants in the foreground, growing in a silt patch near a pond. N.W.T., Banks Island, Sachs Harbour. 24 July, 1981. Gillett 18790. CAN. • Close-up of plants. Plants with green vegetative branching stems 15–20 cm high, and pinkish brown fertile stems with cones. Nunavut, Baffin Island, Iqaluit. July, 2004. Aiken and LeBlanc 04–021. CAN 586494. • Plants in muddy habitat. Pale flesh-coloured, fertile plants between the markers and common in an environment with Bistorta vivipara. Banks Island, Aulavik National Park, wet muddy banks of a side stream beside the Thomsen River. 8 July, 1999. 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 fleshy than those on the sterile stem. Nunavut, Baffin Island, Arctic Bay. 12 Aug, 1927. CAN 3173. • Close-up of sterile stem. Stems with short green spreading branches and appressed teeth with brown margins. Banks Island, Sachs Harbour. 14 July, 1999. Aiken 99–073. CAN. • Close-up of fertile stem. Young fertile cone and leaf teeth with brown margins. Banks Island, Sachs Harbour. 14 July, 1999. Aiken 99–073. CAN. • Close-up of stem with and without chlorophyll. Portion of stem that has chlorophyll at the base and a cone portion without chlorophyll. This is characteristic of var. alpestre. Victoria Island, Mt. Pelly. CAN 273479. • Underground branching rhizomes. 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. Aboveground vegetative stems are less than 5 cm tall, with narrow, E. scirpoides-like stems. Belowground stems are at least five times the length of aerial stems. Ellesmere Island, Borup Fiord, just below 81N. CAN 556099. • Close-up of young cone. Fertile cone, about 1 cm long, that has opened to expose pale yellow sporangia which hang underneath the flattened brown surface of each unit of the cone. Note small flies foraging for spores. N.W.T., Banks Island, Aulavik National Park, Thomsen River. 8 July, 1999. Aiken 99–025. CAN. • Close-up of plants 25–30 cm tall. Herbarium specimen of plants collected at 81N and resembling temperate E. arvense. Ellesmere Island, Head of Tanquary Fiord, growing in the shelter or rocks. CAN 320182. • Young vegetative stem branching. Plant separated from associated moss to show ground-level and aboveground branching and jointed stems. Note that the first internode of each branch is longer than the subtending node on the stem. Nunavut, Ellesmere Island, near John Richardson Bay, 8021'N, 7121'W. Aiken 98–042. CAN. Photograph by Mollie MacCormac. • Arctic Island distribution.


This publication is available on the internet (posted May 2011) and on CD-ROM (published in 2007). These versions are identical in content, except that the errata page for CD-ROM is accessible on the main index page of the web version.

Recommended citation for the web-based version of this publication: Aiken, S.G., Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H., and Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. NRC Research Press, National Research Council of Canada, Ottawa. http://nature.ca/aaflora/data, accessed on DATE.

Recommended citation for the CD-ROM version of this publication: Aiken, S.G., Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H., and Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. [CD-ROM] NRC Research Press, National Research Council of Canada, Ottawa.

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