Equisetum arvense (Field Horsetail)
Species: E. arvense
Binomial name: Equisetum arvense
Synonyms: Allosites arvense, Equisetum arvense. Arcticum, Equisetum arvense fo. Boreale, Equisetum arvense fo. Campestre, Equisetum arvense fo. Ramulosum, Equisetum arvense subsp. boreale, Equisetum arvense subsp. ramulosum, Equisetum arvense var. arcticum, Equisetum arvense var. campestre, Equisetum arvense var. ramulosum, Equisetum boreale, Equisetum caldera, Equisetum campestre, Equisetum saxicola.
Common name: Field Horsetail, Common horsetail. Horsetail, Scouring rush.
Equisetum arvense is part of the ancient genus Equisetum, which was the dominant plant group during the Carboniferous age more than 230 million years ago. . Fossils show the plant has remained unchanged for over 300 million years. It Is native to Europe, Asia and North America and has naturalised in Madagascar, South Africa, South America, Australia and New Zealand. This prehistoric survivor it is one of the toughest weeds to manage.
This plant was introduced into New Zealand in the 1920s and has been classed as an invasive species since the mid-1990s. It is listed on the National Pest Plant Accord preventing its sale, spread and cultivation. In New Zealand isolated infestations have been found at Kawhia, Havelock North, New Plymouth and Wellington. It has become well established and widespread in the Manawatu/Rangitikei particularly on the floodplains of the lower Rangitikei River. From the river it has been spread along roads, walking tracks and to building sites via river gravel used for construction.
Equisetum arvense contains high levels of silica, giving rise another common name: scouring rush. There are no reports of toxicity of Equisetum arvense in New Zealand, but overseas the plant is widely reported as being poisonous to sheep, cattle and horses in both its green state and when dried in hay.
Equisetum arvense is an herbaceous perennial that regrow each spring/summer from a tuber-bearing rhizome. Two types of stems grow from the rhizome annually.
The fertile stems grow in early spring are unbranched, leafless, succulent-textured, off-white, 10–25 cm tall and 3–5 mm diameter, with 4–8 whorls of brown scale leaves and is topped with an apical brown spore-bearing cone 10–40 mm long and 4–9 mm broad and is topped by a spore-bearing cone. Since they lack chlorophyll, they die shortly after releasing their spores.
The sterile vegetative stems arise after the fertile stems die back later in the season, growing to about 10–90 cm tall and 3–5 mm diameter, with jointed segments around 2–5 cm long with whorls of side shoots at the segment joints; the side shoots have a diameter of about 1 mm. Some stems can have as many as 20 segments. These stems which grow each year are grooved and hollow and resemble a horse's tail.
Equisetum arvense has fleshy tubers growing along underground rhizomes singly or in pairs, and can grow from a few centimetres to 2 metres deep in the soil. They store carbohydrates produced by photosynthesis, allowing it to have amazing regenerative capability and making it difficult to control. Attached to the deeper rhizomes are small tubers which remain dormant while the rhizome stays alive. Upon the death/decay of the rhizome, or when it becomes detached due to cultivation or other means, the tubers initiate growth to produce new plants.
In May 2016 The Environmental Protection Authority (EPA) approved the horsetail weevil (Grypus equiseti) as a biological control agent to help curb the weed field horsetail (Equisetum arvense) which It is now classed as an unwanted organism under the Biosecurity Act 1993 as it not responsive to herbicides.
The fertile stems growing early spring
The sterile vegetative stems
A print showing the sterile stems, underground rhizomes and the small tubers.