Mat-forming herb with a branched, horizontal rhizome system reaching some centimetres into the substrate with vertical branches to aerial shoots, forming small or large, loose mats with one or a few shoots arising from each rhizome branch. The uppermost 1–2 cm of the rhizome branches is black, shiny and smooth. Aerial shoots perennial (only one type of shoots), 5–12(20) cm long, 1–1.5(2) mm broad, procumbent, ascending or erect, simple (above rhizome), terminating in a spike with sporangiophores (lost on older shoots). Stems dark green, articulate, angled with 4–8 rounded ribs rugose by low silica tubercles, 5–8 leaves as a sheath at the end of each joint.

Leaves reduced to a fused sheath with free teeth (as many as ribs) in whorls. Leaves green at base, with a broad black band and a narrow white hyaline margin. They are retained, as long as the shoot lasts, as a black sheath with white, withered teeth. Teeth broadly triangular, apiculate with a moderately extended point, but the apical parts are lost with age.

Spikes ovoid, 3–4 mm, initially enclosed within the uppermost whorls of leaves (teeth) and not much emerging from these, with sporangiophores (transformed leaves carrying sporangia) in 4–6 dense whorls. Sporangiophores peltate with an angular end plate participating in a compact outer surface of the spike until the spores are mature and the spike opens with slits between the sporangiophores to let the spores loose. Each sporangiophore carries 4–6 oblong sporangia in a whorl on the inner surface of the plate. Sporangia open by longitudinal slits. Spores globose, green, each with four long, club-shaped bands (hapters), stretching out in dry weather and making the spore mass fluffy and wind dispersed during such conditions. In moist weather the hapters curve inwards making the spore mass immobile.

Sexual reproduction by spores: moderately efficient local vegetative reproduction by rhizomes.

Efficient wind dispersal of spores due to the hapters and the small size of the spores. Downstream dispersal of rhizome fragments is possible.

The genus Equisetum is immediately recognized by the articulate stems and branches and the characteristic spike with angled sporangiophores.

Equisetum arvense is distinguished from the two other species in Svalbard – E. scirpoides and E. variegatum – especially in that the former has annual dimorphic shoots (two different shoot generations), the two latter perennial monomorphic shoots. Even if this difference is very marked, it has often been overlooked and there have been numerous mistakes in identifications. Some additional characters should be consulted. Firstly, E. arvense has branched aerial shoots, mostly yellowish green, the two others simple shoots with dark green colour. Furthermore, the aerial shoots of E. arvense are soft, with intact whorls of teeth on the main stems, whereas those of E. scirpoides and E. variegatum are firm, with withered teeth (often as a bicolorous band in black and white).

Equisetum variegatum and E. scirpoides may be superficially similar but with some significant differences. The shoots of E. variegatum are more stout (> 1 mm), have 4–8 broad ribs and 4–8 teeth, and (a most important character) the uppermost 1–2 cm of the black rhizome branches are shiny and smooth. The shoots of E. scirpoides are nearly always more slender (0.5–1 mm broad), more crowded in dense bunches from the rhizome branches, have 6 ribs or ridges in three pairs but only 3 teeth in each whorl, and the uppermost 1–2 cm of the black rhizome branches are dull and strongly transversely papillose or rugose.

A common species of many site types, both dry and moist ones, sometimes regularly irrigated. It grows in dry to moist heaths, on sediment plains, along brooks and rivers, on lake shores, and in the tussock level in mires. It is very common on frost patterned ground where it grows both in the margins and middle of soil polygons. The species is most common in fine-grained soils but sometimes growing on more coarse textured soils. It is probably rather indifferent as to soil reaction (pH) but perhaps less common in the areas with the most acidic substrates.

Present in all zones and sections but very rare in the polar desert. Fairly common in Spitsbergen and fairly common to scattered in Nordaustlandet and on some of the minor islands (Bjørnøya, Prins Karls Forland). Not recorded from Hopen or Kong Karls Land.

Common throughout the arctic circumpolar and reaching far south into temperate mountains, in Europe to the C European mountains.

A morphologically uniform species throughout the major parts of the northern hemisphere. The only variation assumed to be of taxonomic significance is found in coastal W North America and recognized as ssp. alaskanum (A.A.Eaton) Hultén (see Hauke 1963, 1993; Elven et al. 2011).

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF) Vascular plants. http://panarcticflora.org/

Hauke, R.L. 1963. A taxonomic monograph of the Equisetum subgenus Hippochaete. – Beiheft Nova Hedwigia 8. 123 pp.

Hauke, R.L. 1993. Equisetaceae Michaux ex De Candolle. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 2. Pteridophytes and Gymnosperms: 76–84.