Plant of the Week – October 19th 2026 – Field Horsetail (Equisetum arvense) – Botany in Scotland

Attribution: Carl Axel Magnus Lindman, Public domain, via Wikimedia Commons. Lindman (1856 – 1928) was a Swedish botanist and botanical artist.

The Horsetails (Equisetum species) are the only remaining  genus of a group of plants called the Sphenophytes that arose in the Late Devonian period, 350 to 385 million years ago. They are related to ferns. Some of their ancestors grew up to thirty meters tall. Modern Horsetails look similar to the fossils, and we can therefore regard them as ‘living fossils’. The most common of these in Britain is the Field Horsetail, Equisetum arvense. People in Scotland often call it Marestail but they should not, as another quite different plant is properly called Marestail.

Field Horsetail is a frequent ‘weed’, very hard to eradicate. It features in an interesting book called The World’s Worst Weeds (Holm et al. et al 1991). What has it done to deserve such a reputation?

This image shows the general structure of the vegetative shoot in a well-developed plant with its whorls of branches and its grooved stem. Image: Chris Jeffree, taken in Estonia.

It is a perennial plant with deep horizontal and vertical rhizomes from which it sprouts its characteristic ‘Christmas Tree’ form. Some remarkable tales are told about the rhizomes. According to one report, a piece of rhizome, 10 cm in length, planted in a growth room, produced, in one year, a total of 64 metres of rhizome in a vertical direction through branching. Other reports say that horizontal rhizomes can reach a length of up to 100 metres under field conditions (see Cody and Wagner 1980). I’ve sometimes tried to dig out entire rhizomes, but failed because they are so deep. There’s is a subterranean life, string-like and impossible to excavate, dark brown and slender, hard to see. We imagine its ancestors lurking at great depth, surviving for aeons the fires, floods, asteroid strikes and bursts of cosmic radiation that would have laid waste the surface vegetation. But they were safe and unscathed – perhaps these cataclysmic events made useful mutations and helped them to adapt, evolve, and survive to become the weed we know today.

The sporophytes emerging in early spring from a municipal garden bed. Image: John Grace, taken in Ballantrae.

You may see, in the spring, brownish stems bearing cones. Within these cones the spores develop, and are dispersed. In the fertile soils of gardens these structures rarely appear – instead the green vegetative shoots emerge as soon as the soil warms up in the spring.

Close-up of the cone. Whorls of stalked, umbrella-like (peltate) and hexagonal shield-shaped structures are attached perpendicularly to the central axis. Elongated sporangia hang downward from the underside rim of each peltate sporangiophore disc. Spores produced inside the sporangia possess ribbon-like, hygroscopic appendages called elaters that coil and uncoil in response to changes in humidity, helping the spores disperse through the air.

The green plants emerge from the underground rhizomes. They consist of a regularly branched stem with ‘leaves’ reduced to tiny scales, fused into a collar-like sheath around the joints (nodes) of both main stems and side branches. These leaves don’t look very useful for absorbing light; their role is mainly to protect the developing branches. The photosynthetic function is performed by the green stems, and the main season for photosynthesis is the summer, when the whole structure can be 50 cm tall or more – in that period the sugars of photosynthesis are being transported to the rhizomes and turned into starch, ready for next year.

Leaves are reduced to pointed scales. The scales are fused together at the base into a ring that wraps around the stem. These leaves contain little or no chlorophyll. Image: Chris Jeffree.

Can we be sure that these scales are really ‘leaves’ and what is the definition of a ‘leaf’? One important fact is that in the sister genus Sphenophyllum from the Upper Carboniferous period (323 to 299 million years ago) and now entirely extinct, there were proper leaves in whorls – they were broad flat structures. It looks like the leaves were reduced to become scales during the evolution of today’s Equisetum.

Hand-cut section of the main stem, showing hollow stem and surrounding air spaces. The vascular bundles (for transport of water, nutrients and sugars) are the brown tissues. The chlorophyll shows as green. The shallowly-grooved stem can be seen as wavy edges. Image and section-cutting: Chris Jeffree.

I’ve read that the rhizomes also have tubers attached, looking like tiny potatoes. We haven’t seen the tubers – I believe they don’t develop in highly fertile garden soil. They store starch, much like a potato does, and assist the spread of the plant. As well as asexual spread by rhizomes and tubers, there is also a sexual process, described below.

The sexual reproductive system resembles that of ferns: the above-ground brownish spear of early spring is the ‘sporophyte’. Its job is to make spores. When spores are deposited to soil in a moist, damp environment, they germinate to make tiny green structures, each called a ‘prothallus’, just a few millimetres across. These are the ‘gametophytes’ and their role is to make the gametes. They shed flagellate sperms which swim in films of water to the eggs and fertilize them to form zygotes. Then a new generation of sporophytes sprouts forth.

The shoots have emerged through asphalt and they are rapidly expanding to form a canopy. Image: Chris Jeffree in Leith.

This plant is very tough. Its shoots often penetrate the asphalt of pavements. Some people try to eradicate the weed from their garden by applying the herbicide glyphosate. But the above-ground parts have a waxy cuticle and the droplets just run off. Standard advice is to ‘roughen up’ the cuticles by stamping on the plant first. Another control method is to cover the ground with black plastic film for 3 or 4 years. I don’t mind getting down on my hands and knees and teasing out the rhizomes with a fork, but there are always some pieced left. My advice to people with a small garden is to take scissors and cut off the green shoots as they emerge. Eventually, the rhizomes will starve to death.

British and Irish distribution of Equisetum arvense from BSBI/Maps. There are only a few 10-km squares where the plant has never been recorded.

Equisetum arvense is a native plant, occurring all over Britain and Ireland in a variety of habitats. The BSBI Atlas 2020 gives this summary of habitats as: “riverbanks, fixed dune grassland, sea-cliffs and montane flushes, but also frequent in anthropogenic habitats…it is now frequent on pavements, roadsides, railways, paths, soil banks and in highly disturbed habitats such as waste ground, quarries, gardens, allotments and arable land”.

Global distribution of Equisetum arvense from GBIF. This projection shows how the plant occurs almost everywhere in the northern hemisphere. There are a few records in the south, including New Zealand.

This plant is much more than an arable weed. It is packed with useful chemicals: flavonoids, glycosides, organic acids, alkaloids, sterols and others, many with valuable pharmacological properties. This is not my field of expertise – however, I did find a scholarly review by Luanda et al (2023) which you may be able to view and download here.

Equisetum arvense has a traditional use in the kitchen, as a scouring device to clean pots and pans. It works because the plant tissues contain silica (tiny sand particles).

The base of the plant, showing emerging buds. Image: Chris Jeffree.

Many plant species accumulate toxic metals from the soil (they are called ‘hyperaccumulators’) but  Equisetum arvense has the special reputation of being able to accumulate gold. One early paper states a concentration of 4.5 oz. gold per ton. An oz. (=ounce) is 28.3495 grammes, so that’s 0.013%. Don’t rush out and grab armfuls to get rich – obviously the soil has to have gold deposits. The main value of this hyperaccumulation is for prospectors to detect the location of gold and other metals.

As with many plants, there are culinary traditions as revealed by Google’s AI:

Japan (Tsukushi): In early spring (March to April), the young, brown, fertile spore-bearing stalks—resembling small, scaley asparagus—sprout from the ground. Known as tsukushi, they are a celebrated seasonal delicacy representing the arrival of spring. They are traditionally prepared as Tsukudani (simmered in soy sauce, mirin, and sugar) or fried as crisp Tempura.

North American Indigenous Peoples: Historically, various Native American and Inuit groups consumed the subterranean, starch-rich tubers/nodules (which reportedly taste mildly sweet) as well as the very tender young shoots.

Europe: Historic records mention field horsetail being consumed in early spring by agricultural workers or children as a forage snack in parts of Northern and Eastern Europe.

An on-line offer of dried Equisetum arvense

It is however a poisonous plant, highly toxic to livestock, particularly horses. It contains contains thiaminase, which destroys Vitamin B1 (thiamine) in the body. Thiamine is needed for central nervous system function and extracting energy from nutrients, so its deficiency leads to a condition historically known as “bracken staggers” or horsetail poisoning. In food preparation, thiaminase is denatured by cooking. I am unsure about herbal preparations.

Despite its toxicity, there are many herbal preparations. Examples: offers of Horsetail tea and food supplements on Amazon.com, and over-the-counter tincture can be purchased at Napiers of Edinburgh. Yes, the sale of herbal remedies is regulated in the UK, primarily by the Medicines and Healthcare products Regulatory Agency (MHRA) and local Trading Standards. And I do like the idea of the Japanese Tsukudani.

There are several other equisetums in Britain and Ireland. We showed images of most of them last year. You can find them here.

References

Benedict, R. C. (1941). The gold rush: a fern ally. American Fern Journal, 31(4), 127-130.

Cody W. J. and Wagner V. 1980. The biology of Canadian weeds. 49. Equisetum arvense L. Can. J. plant Sci. 6L:123-133

Greger M and Landberg T (2024). Equisetum arvense as a silica fertilizer. Plant Physiology and Biochemistry, 210, 108606.

Holm LG et al. (1991). The world’s worst weeds – distribution and biology. Florida, Krieger

Lee, J. (2025). Deep-Time Evolution of Tubers in Equisetum and the Broader Sphenophytes. International Journal of Plant Sciences, 186(5), 373-392.

Luanda, A., Ripanda, A., & Makangara, J. J. (2023). Therapeutic potential of Equisetum arvense L. for management of medical conditions. Phytomedicine Plus, 3(2), 100444.

Pratt, M. K., Westbrook, A. S., & DiTommaso, A. (2024). Reproductive strategy, management, and medicinal uses of field horsetail (Equisetum arvense). Weed Technology, 38, e47.

©John Grace