Friday, 15 November 2013

In praise of ivy.

Let's face it, ivy can be a nuisance. When we moved into our current house one wall was clad with it and had got completely out of hand. To remove it was beyond me, given the height it had reached, and I had it professionally removed - not a cheap job. From time to time in recent years, trees top-heavy with ivy have crashed down across the A361, blocking it for several hours. Lichenologists and bryologists hate it for the way in which it smothers tree trunks, destroying the surface as a habitat for lichens and mosses respectively. And yet...

Ivy belongs to a plant family called the Araliaceae. My copy of "The Families of Flowering Plants" by John Hutchinson, published in 1959, suggests the family has 250-260 members; more recent floras put the number at around 1500 species. This is partly because studies in tropical rain forests (it is largely a tropical and subtropical family) have led to the discovery of many new species. But it also reflects the fact that the parameters for defining the family are far from clear and it is likely that, as the genetics of the family are unravelled, the figure could change drastically again.

Ivy, our sole member of the family, is Hedera helix. I assume that this suggests that the plant stems form a helix as they grow upwards in the manner of runner beans, but I have rarely seen them adopt a helical habit. The species is found throughout Britain and from Norway across to Iran but is absent from Russia.
Ivy scrambling across the woodland floor.
Byfield Pocket Park, 15 November, 2013

So, what can be said in its favour? It is reasonably hardy though not bone-hardy; it will flourish in dry and gloomy conditions where little else can survive and it has some attractive forms with bright yellow variations of the leaves. So much for its gardening merits. What of relationship with other wildlife? A song dating from 1943 called Mairzy Dotes tells us that:

                        Mares eat oats and does eat oats 
                        And little lambs eat ivy.

In fact the plant is occasionally browsed by deer and cattle and has been used as emergency fodder over many centuries. Only one insect (Dasineura keifferi) forms galls on the developing flower buds and although caterpillars of the Holly Blue butterfly will feed on the foliage, as far as I am aware not one insect mines the leaves. For such a widespread plant this is a remarkably low usage. However, that is not the whole story. 
A calliphorid fly feeding on ivy nectar.
Byfield Pocket Park. 15 November, 2013

Ivy begins to flower in mid August and at the time of writing is still in flower in our village pocket park. The flowers are dioecious, that is, there are separate male and female flowers. In the third photograph the male flowers can be clearly seen beside the now-fruiting females. These flowers provide a copious supply of nectar and are besieged by many insects including hover flies, bees and even today (15 November) wasps were gorging on this energy-rich liquid. 

When Shelley, in his poem "Poet's Dream", wrote of "The yellow bees in the ivy bloom" * he was writing of something which must have been going on for, probably, millions of years. The flowers eventually lead to fruit which slowly ripen to be available to birds as the year draws to a close. Even now, with some branches bearing flowers, others bear almost-ripe berries. It is a clever strategy because, in late winter, hungry birds will gorge on these fruit, ensuring widespread dispersal of the seeds via their droppings.

Ivy with ripening fruit. Byfield Pocket Park
15 November, 2013
In my first photograph, showing ivy sprawling across a woodland floor, the leaves are of the classic shape as shown on millions of Christmas cards. However, it will be seen that the flowering/fruiting branches bear leaves of quite a different shape, being of a simple, more or less elliptic shape and far glossier than the palmate ones.

So, a pest or an asset to the countryside? As with so many questions of this type, it is a matter of opinion but during recent decades ivy seems, over many areas, to be getting out of control. Perhaps we should return to using it as fodder.

* In this year of Benjamin Britten's birth centenary I should mention that he set this poem beautifully for tenor voice in his "Nocturne", opus 60) 

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