Mistletoe

At this time of the year Mistletoe, Viscum album, tends to be the subject of magazine articles, with much discussion of its ritual significance and so on. (A pupil of mine once assured me that Christ, at his birth, received presents of gold, frankincense and mistletoe.) But it is worth considering from a purely botanical angle as it is, rather obviously, a curious plant, but also a very interesting one. It has at various times been placed in the Loranthaceae family and the Viscaceae family, but it is now generally agreed that is related to the sandalwoods in the Santalaceae family.

Mistletoe in apple trees: drawing by Christine Hart-Davies

The distinguished taxonomist, John Hutchinson, in his two-volume work 'British Wild Flowers' (1955 edition) described it as 'truly parasitic' but, fifty years later, few botanists would accept this. Admittedly it could not survive without its host tree which, in Britain is usually apple, hawthorn, lime or poplar (recently I travelled by TGV down to Auxerre in France and, from the train window saw huge quantities on poplar) but it is perfectly able to perform photosynthesis via its pale yellow-green leaves and all it takes from the host is water plus a few minerals. It is surely best described as a hemi-parasite.


In Britain it has three centres of distribution with smaller concentrations elsewhere. By some distance the British heartland of this species is the Herefordshire/Gloucestershire/Shropshire area and yet, not far away, in for example Monmouthshire, North Devon and Wiltshire, it is quite rare and I know of no obvious explanation for this. There are secondary centres of distribution in Surrey and Somerset.


Mistletoe is dioecious, that is, the plants are either male or female, and on the face of it this is a considerable disadvantage as a single seed, deposited on a tree by, perhaps, a thrush, would be isolated. However a single seed is poly-embryonic, that is, it can produce several seedlings and it appears that these may be a mixture of male and female plants. Incidentally the Mistle Thrush may indeed be a frequent distributor of the seeds and it is significant that this bird's Latin name is Turdus viscivorus, which may be translated as 'the mistletoe-eating turd thrush'. However, a seed I 'sowed' on an apple tree in Byfield produced only a male plant, with no sign of siblings. (Incidentally this is ideally done in about March.) In Northamptonshire it is a rarity but a good place to see the species is at Kingsthorpe Recreation Ground, in Northampton, where hybrid limes, Tilia x europaea, once carried somewhere in the order of a hundred plants although a recent check suggested a number have disappeared. Elsewhere in Northampton I have noted it on False Acacia, Robinia pseudoacacia, trees in the Weston Favell area of the town. Although rare in Northamptonshire John Clare seems to have been familiar with it, writing:
                                   And on old thorns the long-leaved miseltoe
                                   Regains fresh beauty as the parent dies!
                                                                               Shepherds Calendar, 1827
It will grow on native oaks but there it is extremely rare and Keith Spooner, writing in the journal Cecidology, vol 31, 2, could only find about five examples still extant. A small number of records in Britain are known from red oaks but these are North American species introduced into parks and so on.
Pliny the Elder recorded that mistletoe berries in a drink would make a barren animal fertile and this idea may be associated with a belief in ancient Greece that mistletoe functioned as the genitals of the oak. Of course, lopping it off with a sickle was regarded as ritual emasculation. This association with fertility is the original idea behind 'a kiss under the mistletoe'. My old copy of 'Potter's Cyclopaedia of Botanical Drugs and Preparations' describes it as 'a tonic'; I suspect that this is a euphemism for aphrodisiac!
I am getting away from my intention, expressed in the opening paragraph, of sticking to the botanical interest of mistletoe. The genus Viscum consists of 80-100 species found worldwide with the exception of the Americas, but even there it has been introduced to California, where it has spread steadily, and to Vancouver Island. As a parasite - albeit in only a limited way - it may not be welcomed everywhere.
The habit of Mistletoe is distinctive for it forms unmistakeable, almost spherical bunches, making a plant easy to spot and rather different from the witches' broom growths often seen on birch.

The rather drooping shape of Witches' Brooms on birch.

Daventry, 13 December, 2016

The shape of a mistletoe clump is due to its dichotomous growth. Each year every branch simply forks, producing two leaves on each new extension. As this generally happens every year it is possible, by counting the number of times a branch has forked, to roughly establish the age of the plant.


Mistletoe on Hybrid Lime, Kingsthorpe Recreation Ground, Northampton.

17 December, 2016. Note the more spherical shape of the clump.

Clumps can exceed four feet in diameter and I have certainly seen some with this sort of dimension on the continent, but British examples tend to be smaller. I continue to be on the lookout, as winter is the optimum time to survey your neighbourhood for this remarkable plant.




Tony White: diaea@yahoo.co.uk