Monthly Archives: October 2015

Wednesday Weed – Broad-leaved Dock

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…..

Broad-leaved Dock (Rumex obtusifolius)

Broad-leaved Dock (Rumex obtusifolius)

Dear Readers, on Sunday I made a brief foray into Coldfall Wood to see how autumn was shaping up – after being away in Canada for a fortnight, and then working away from home for a week, I was eager to fit in a quick visit. The area around the winter pond was full of bulrushes and Michaelmas daisies, but the dominant plant was this one, broad-leaved dock.

I know nothing about docks of any kind, except that they are a) the cure for stinging nettle hives if the leaves are rubbed onto the affected area (my dad assures me that dock always grows close to nettles for just this purpose), and b) that they are long-rooted and hence a nightmare to dig out once they become established. My research for this piece has revealed that the taproot can be up to five feet long, which makes me wish that I’d thought about tackling the dock next to my rowan tree a bit earlier. Like, several years ago.  But here in Coldfall Wood, in the damp claggy soil of the pond, the broad-leaved docks seem to be thoroughly enjoying themselves. Their rusty-red seedheads have a kind of ramshackle beauty about them.

IMG_4549One way to tell broad-leaved dock from the other members of the family is to have a look at the leaves. At the base, they are distinctly heart-shaped – the leaves of most other docks are strap-like. The fresh young leaves can be eaten like spinach, although grazing animals will avoid them, and the taste is said to be unpleasant. Furthermore, the plant is high in oxalic acid, so eating it should be avoided by those prone to kidney stones or joint problems. The leaves have been used to wrap cheese and butter (it is believed that this will keep the food fresher for longer), and adding a few dock leaves to a pot of water is said to make it come to the boil more quickly. This last belief is rather intriguing: when I have more time, maybe I’ll try a scientific experiment in the kitchen to see if there is something about dock that lowers the boiling point of water, or whether throwing anything into a pot of water would work as well – I’ve certainly seen water suddenly boil over when I’ve added salt or oil. The world is full of mysteries, to be sure.

IMG_4538This is a native plant in the UK, but like so many others it can now be found in North America too. Even in the UK it is designated as an ‘injurious weed’ in the 1959 Weeds Act (who knew there was such a thing?), and it is one of five weeds (the others are Curly Dock, Common Ragwort, Spear Thistle and Creeping Thistle) that the Secretary of State can insist are controlled even on private land. We have already mentioned the plants’ deep tap-root, but as it can produce 60,000 seeds wind-dispersed seeds per year, and as these seeds can survive for up to 50 years (due to a chemical that prevents microbial breakdown), I can see how it could be a problem on cultivated land. However, in my experience this is a plant that pops up in damp, claggy, over-grazed fields, where the competing plants have already given up the ghost. The plant is a symptom, rather than a cause.

In spite of it being part of this ‘hall of fame’ however, broad-leaved dock has a variety of medicinal uses, in addition to its efficacy with nettle stings (to which I can personally attest). A tea made from dock root was said to cure boils, and the leaves have been used to soothe burns and abrasions. The Iroquois Indians used a tea made from the plant as a contraceptive (though how successful this was is not known). The seeds have been used as a cure for tuberculosis and stomach infections, and also as a spice, although the recipes that I’ve seen are for curled dock (Rumex crispus) rather than for broad-leaved dock.

IMG_4541Broad-leaved dock is a member of the Polygonaceae family, which includes two other plants that have already been featured on the blog:  Redshank, and Japanese Knotweed. As you can see, it is a family of plants that can be problematic from a human point of view. I prefer to think of them as a family of survivors and opportunists, who will flourish when most other plants would fail. When I look at a stand of broad-leaved dock, I wonder if I am looking at a potential post-apocalyptic plant, one that will be here long after we are all gone. For some reason, I find its resilience strangely reassuring.

IMG_4542

A Tale of Two Squirrels

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A Grey Squirrel (Sciurus carolinensis) munching on hawthorn in my London back garden

Dear Readers, I have always been fascinated by the diversity of individuals within a single species. To take one example: why do pigeons come in such a variety of colours? But something that I’ve never quite gotten to the bottom of is why the majority of Grey Squirrels in London, UK, look like the little chap in the photo above and yet Grey Squirrels in Toronto look, well, mostly like the animal below, when they both belong to the same species.

Torontonian Grey Squirrel

Torontonian Grey Squirrel (also Sciurus carolinensis)

Not all the Grey Squirrels in Toronto are black, but from my observations I’d say that they make up at least 80% of the population. In London I have yet to see a black squirrel, although I do know that a tiny population exists.  So why this difference between the two countries? To begin with, I had a little look at genetics. And to make things easier going forward, I’ll use ‘grey squirrel’ and ‘black squirrel’ to refer to the colour of animals of the same species, the Eastern Grey Squirrel (Sciurus carolinensis).

Two grey-coloured squirrels cannot make a black squirrel – each animal has two copies of the ‘normal’ pigment gene. A squirrel with one copy of the ‘mutant’ black gene and one copy of the ‘normal’ grey gene will be a brown-black squirrel, like the rather handsome creature below.

Black-brown squirrel from Collingwood, Ontarioi

Black-brown squirrel from Collingwood, Ontario

A squirrel with two copies of the ‘mutant’ black gene will be jet-black.

IMG_4442These colourings should not be mistaken for physical features that result from something that happened to the animal. For example, the black squirrel below, seen when I was with my friend Michelle at the Royal Botanic Gardens in Burlington, is jet-black with a white spot on the tail, which may be the result of injury or of some kind of skin damage. Whatever the reason, it gives the squirrel a rather attractive Cruella de Ville look.

IMG_4437 (2)IMG_4438 (2)

So, the question remains: why are squirrels in the UK largely grey, and the squirrels in Ontario (and many other parts of North America) largely black? There are several theories.

One is that the black ‘mutant’ squirrels were actually the prevailing colour variation prior to the arrival of Europeans in the 16th Century. The animals’ darker colour may have helped to camouflage them in the densely canopied old-growth forests, but when these started to be cut down, the  advantage shifted towards the grey squirrels in many areas. The remnant black populations, such as those in Ontario, may have survived because more of the northern forests remain, but also because black colouration absorbs and retains more of the sun’s heat, meaning that the animals can be more active and find more food during the long, cold Canadian winters.

As you will remember from previous posts, the Eastern Grey Squirrel is an introduced species in the UK, and the vast majority of animals are of the ‘normal’ grey colouration. If we think back to our discussion about genetics earlier, it is likely that any black animals seen are descendants of imported captive animals, rather than the mutation occurring simultaneously in the population. However, having said this, there are now large populations of black squirrels in Stevenage, Letchworth and Hitchin, where they are said to make up fully 50% of the resident squirrels. One further theory concerns female sexual preference: given a choice between a grey male squirrel and one with black colouration, it may be that the females prefer the latter, which would result, over time, in an increase in black squirrels over grey-coloured ones. This is not as unlikely as it sounds – the peacock’s tail, the long neck of the Giraffe-necked Weevil and the extravagant dances of birds of paradise are an indication to the female that the male is healthy, and hearty, and free from parasites – only the most hale of individuals can sustain such extravagant accouterments. So, does the glossy coat of a black-coloured squirrel give a clearer indication to the female that her partner-to-be is in the first glow of health, and will she therefore prefer him, all other things being equal? It will be interesting to see how the squirrel population develops here in the UK. Maybe, one day, London’s squirrels will be as diverse as the humans who surround them.