Every Wednesday, I hope to find a new ‘weed’ to investigate. My only criterion will be that I will not have deliberately planted the subject of our inquiry. Who knows what we will find…..

Dear Readers, during a long-overdue walk through St Pancras and Islington Cemetery last week, I spotted some mare’s tail (Equisetum arvensis) growing on a single grave. I wonder what the conditions were to produce such a crop, but only on this one site? Truly, the ways of the plant kingdom are a mystery, although I note that mare’s tail was once said to be an indicator of underground water. The cemetery is studded with such streams, so perhaps this is an explanation

At first glance mare’s tail resembles grass or a rush, but closer inspection shows that it is actually a living fossil that has been in existence for over 100 million years. Its structure is unique to this family of plants, with a whirl of spikey ‘leaves’ around each stem. Back in the good old days of the Carboniferous period, mare’s tail could grow into a magnificent tree 30 metres tall, and the fossils from these plants can sometimes be found in coal deposits, for Equisetum species formed a large part of this fossil fuel. These days Equisetum plants are of more modest stature, but are still worth a close look, because nothing else like them still exists. The giant dragonflies that I mentioned in my post last week would have been very familiar with these plants.

In German, mare’s tail is known as Zinkraut or tin-herb, because the stems contain silicate, absorbed from the soil in a way that is very unusual in plants. Mare’s tail is useful as an abrasive and cleaning-agent for metal, especially tin, and another English name is scouring-rush. A member of the Equisetum family is used in Japan in the last stage of woodworking, producing a finer finish than any sandpaper.

This is one of those plants that looks very different as the seasons pass, and this is because it produces two different kinds of growth. In spring, the fertile shoots look more like fungi than plants: in fact although I’m familiar with the summer foliage of mare’s tail, I was completely flummoxed by the buds when I visited Canada last year. These are what enable the plant to reproduce, but don’t photosynthesise.

As the year goes on, the plant develops photosynthetic foliage, both to survive and to create the conditions for reproduction during the following spring. Both kinds of shoot come from a complicated network of rhizomes under the soil.

But by autumn, all that’s left are a few of the main whorls of stems.

The plant proved to be an inspiration to the father of logarithms, John Napier. I remember using my logarithmic tables for O level Maths way back in 1976, but these days I imagine it’s all done with computers, and logarithms have gone the way of the slide rule. As you will probably remember, a logarithmic scale is a nonlinear way of describing something which has a very wide range of values. For example, the Richter Scale for measuring earthquakes is a logarithmic scale: an earthquake with a value on the Richter Scale of 6 is ten times stronger than one with a value of 5.

Napier noticed the way that the nodes on the mare’s tail got closer together as they approached the tip of the plant. That’s difficult to see on the older plants in my photos, but have a look at these fresh young greater horsetails, and you’ll see what caught his eye. I love the way that patterns in nature influence both scientists and artists.

Incidentally, Richard Mabey (in Flora Britannica) reports that in some places, mare’s tail is known as ‘Lego Plant’ because it comes apart at the nodes, and can be put back together again. It can also be used as a fungicide – mare’s tail boiled in water has been used with some success against rose mildew.

In herbal medicine only the photosynthetic summer parts of the plant are used, usually as an astringent or for the treatment of nosebleed.

I would be remiss if I didn’t note that mare’s tail is sometimes considered to be a most pernicious weed. The RHS describe it as a plant that is ‘ is an invasive, deep-rooted perennial weed that will spread quickly to form a dense carpet of foliage, crowding out less vigorous plants in beds and borders’. Those rhizomes have got a lot to answer for! The RHS notes that simply pulling the plant up will just make things worse, as the plant can regenerate from the tiniest bits of root, (although if you are going to attempt this, the best time is when the fertile shoots appear in April) and suggests a range of chemical options. It also suggests battering the plant with a rake before applying the weedkiller, which could be therapeutic if nothing else. I have rather a ‘live and let live’ attitude to perennial weeds in my garden, which involves pulling them up or cutting them back if they get too enthusiastic, but tolerating them in small numbers. Life is too short for all-out war, surely.

I have been unable to find any works by the Old Masters (or indeed Old Mistresses) of mare’s tail, but here is an illustration of the Cretaceous period, featuring a most splendid equisetum on the right hand side, plus various assorted reptiles sunning themselves on the bank. I note some Gingko trees as well, which could well be another Wednesday ‘weed’ at some point in the future. You’ll note that my definition of ‘weed’ is becoming more and more expansive as I tick off the actual ‘weeds’ in my half-mile territory. Well, after almost four years I have already featured nearly 200 of the little darlings.

And for the poem? I have a humdinger this week by Anne Stevenson, who traces the path from mare’s tail through coal to the mining communities that extracted it and are now gone. As you know, I don’t cut and paste poems from living writers, because this is how they earn their crust. But please do click through here to read the poem, which is full of wonders. You won’t be disappointed, I promise.

Photo Credits

Photo One by By Alex Lomas – Equisetum arvense, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=44451880

Photo Two by By Namazu-tron – Self shot by mobile phone, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2935195

Photo Three by By F. Lamiot (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons

Photo Four by By MPF (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Photo Five by By Rror (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons