Equisetum arvense L.

Aerial stems dimorphic. Sterile stems erect, 100–800 mm high, 1–5 mm in diameter, green, usually regularly branched, with undivided lateral branches arising in whorls; main stem occasionally producing terminal strobili in mid-summer; stem ridges nearly smooth; grooves 4–14; central hollow < half the diameter of the stem; leaf sheaths green with brown tips, 4–10 mm long. Fertile stems 95–275 mm high, 1–3 mm in diameter, pale brown, lacking chlorophyll, unbranched; normally appearing in spring before the sterile stems, and dying after shedding spores; leaf sheaths pale green or brown with darker teeth, 9–22 mm long. Strobili 4–40 mm long, 5–10 mm in diameter, apices obtuse.

Equisetum arvense is recognised by its dimorphic fertile and sterile stems, its abundantly branching vegetative stems that have uniformly green leaf sheaths with 4–14 grooves, and its obtuse strobilus. It is easily the most common of the species in New Zealand, frequently dominating river-banks and other sites where it has become established.

Equisetum arvense occurs most frequently along muddy banks of lakes and rivers, in river shingle and sand, along drains and the edges of swamps, in damp grass, in wet dune hollows, around shingle piles, and as a weed of cultivation in urban areas. It is an aggressive weed in sandy and muddy soils because of its extensive underground rhizomes, and frequently excludes other vegetation. It is almost impossible to eradicate once established, and is not readily susceptible to chemical control (James & Rahman 2010). In urban areas, stems are capable of pushing up through tar seal.

Atkinson (1922, p. 290). Voucher: AK 110803, 1922

Equisetum arvense in the Northern Hemisphere has been documented by Hauke (1967), and its coning behaviour in New Zealand described by Brownsey et al. (1985). In New Zealand E. arvense is an Unwanted Organism.