66 How galling
The mysterious little growths that appear on our trees and shrubs contain a miniature world of wonder, finds Steven Desmond
The little growths that appear on our trees and shrubs contain a miniature world of wonder, finds Steven Desmond
One of the minor pleasures of walking in the countryside in summer is the discovery of familiar novelties of plant growth along the way. These pleasures include the faintly weird and wonderful world of galls of various kinds, which sprout from wayside trees and shrubs. These curious growths barely register on the consciousness of most people, but, for those in the know, there’s a little world of wonder here, worth exploring in a mind-broadening sort of way.
It would be easier for me to explain these phenomena if they could be categorised neatly by botanists and entomologists under a series of headings, but galls always seem to end up in the ragbag department of odds and ends in any serious book of pests and diseases.
There are two main reasons for this. Firstly, galls can be caused by miniature wasps, mites, fungi, bacteria and a whole range of random growth developments, which scientists like to describe as ‘imperfectly understood’. Secondly, as a general rule, galls don’t really cause significant damage. Some people worry about their appearance on favourite plants and wish contractors to come and put things right.
The wise advice, by and large, is that galls are just part of the proverbial rich tapestry of life, cause negligible harm and aren’t worth worrying about. It’s better to think of them as subjects for enjoyable conversation. The greatest variety is, of course, to be found in ancient woods and hedgerows, where ecosystems are at their richest, but these growths often turn up in the least promising locations, suggesting that they’re more resilient than we might suppose. And there may be more to it than this.
One of the most familiar galls is the oak apple, that marble-sized, brownish growth that attaches itself to the twigs of oak trees, especially rather scrubby little ones. This is a classic case of a growth reaction caused by a tiny wasp, which we wouldn’t recognise as such if we saw one, that lays its eggs in the twig tissue. If you were to slice an oak apple in half, you would find that it is riddled with wiggly tunnels, called galleries, in which the grubs of the next generation are busy munching away. If you then toss the oak apple aside, the blue tits of this world will thank you for your co-operation.
There was a time, however, when this humble organism assumed a much greater significance. In 1660, parliament called upon the nation to celebrate ‘forever’ the Restoration of King Charles II each year on May 29, an event generally known as Oak Apple Day (‘ Bring back Oak Apple Day’, May 27, 2015). This shindig has largely, although not entirely, lapsed into desuetude, but it’s worth remembering that those who failed to adorn their persons with a sprig of oak, ideally with ‘apple’ attached, on the day were once pelted with eggs and thrashed with nettles.
A particularly handsome form of this kind of gall is Robin’s pincushion, found on native hedgerow roses in the summer and sometimes on our garden shrub roses. Many people will know this
As a general rule, galls don’t really cause significant damage
apparent random bundle of pinky-red moss, which hangs out of hedgebanks on great, thorny arching shoots and unfailingly attracts attention. Its function is pretty much the same as the oak apple. Its common name, however, invests it with a special mystery. Of course, nobody knows to whom ‘Robin’ refers, but the suggestion is often Robin Goodfellow, that mischievous character who lurks in the other world of fairy tales. It might not be such a good idea to cut this one in half and chuck it away, lest your milk curdle—or worse.
One gall that occurs every few years and is of some concern to us all is the knopper gall. This is another mini-wasp job and has the effect of distorting, indeed contorting, acorns so that they’re barely recognisable and renders them useless as seed. It affects the native oak, but is more commonly seen on the acorns of the turkey oak, Quercus cerris, of which it makes a complete mess. There are years in which it’s very common, typically followed by years in which it is absent.
Another gall familiar to anyone walking in woods is the witches’ broom. This can readily be seen hanging in the crown of a birch tree and is also found on other native trees, including hornbeam. A scientist will tell you that it’s a random proliferation of shoots from a single point, caused by a disturbance of stem tissues prompted by processes that are as yet—you’ve guessed it— imperfectly understood.
Others of a more vivid turn of mind will tell you that these apparent aerial birds’ nests halfway along a branch are the manifestation of something altogether more sinister. You decide. In some cases, a whole tree can be festooned with random bunches of black shoots and it’s easy to see how a certain significance could be read into it all.
Among the less mysterious, but commonly encountered galls is the nail gall, often found on the leaves of lime trees. This well-named gall raises scarlet points on the surface of the leaves, looking dramatic against their bright-green surface, as if some cruel wight has perversely pushed red-hot nails through the leaf from below. People often express dismay, fearing the worst, but, in fact, there’s no cause for concern.
It’s all part of the everyday life of the lime tree and, like most galls, offers the superficial but pleasant bonus of being something to look out for on a country walk, for those who like that sort of thing. What a sad day it will be when everything around us is perfectly understood.