66 How galling

The mys­te­ri­ous lit­tle growths that ap­pear on our trees and shrubs con­tain a minia­ture world of won­der, finds Steven Des­mond

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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.

Part of Na­tureõs rich ta­pes­try: a hedgerow tree fes­tooned with Ôbirdsõ nestsõ of witch­esõ broom

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