Friday, 10 December 2010

Ivy – Helix in more than name

Hoar frost ivy in Sussex
When I decided to put something together on a Christmas plant I chose ivy largely because I was intrigued by what I might discover, only to discover that it has had little more than cursory mentions amid hinted at deeper stories.  Ivy as a Christmas decoration is often twinned with holly, but much folklore prefers it used for outdoor rather than indoor decorations because it has some awkward pagan overtones.  Ivy is also a symbol of Bacchus and its use in garlands and head decorations was popular because it was believed to ward off the ill effects of too much alcohol.  This is very appropriate for modern Christmas Days when many people across the country start the day with a Buck’s Fizz and continue drinking until the end of the Christmas meal.  In the early Christian church it was not so highly thought-of and it would be interesting to know what store the temperance movement might set by its continued use as a Christmas emblem.

Telegraph pole, Ireland
Ivy was named Hedera helix by Carl Linnaeus in his Species Plantarum of 1752.  Helix as a word dates back at least to the 1560s and almost certainly well before, referring to ‘spiral’ in both the Latin and the Greek.  In modern parlance, of course, we think of the helix of life, of the description of DNA and its double helix form.  A close look at the form of ivy as it climbs a tree shows a spiralling growth and multiple stems intertwining as they progress up the tree.  In a similar species, the strangler-fig in the rainforest, this action is far less benign than the picturesque image we have of the ivy.  In the rainforest trees are used as support for the young and semi-mature vine, until it reaches a weight and height that can be self-sustaining after which point the host tree is allowed to rot and die away.  The weight of the ivy can bring down a less robust tree, but strangulation is not in its primary vocabulary.

Ivy clad wall, Ireland
Ivy as a plant grows well almost anywhere in temperate climates.  It is pretty robust in dark, dank and northern aspects as well as being remarkably tolerant of low rainfall and pollution.  This has made it consistently popular as a plant in gardens and public spaces for centuries.  In  Europe in medieval times it was part of the palette of plants, including vines, used to drape over trellises and arbours, providing a manageable structure to the green areas of the time.  It is  used frequently to cover walls and fences.  At periods through history it has been used as a wall covering for houses, where it was considered to be beneficial in the retention of warmth because of the outer area of the plant having the leaves, inner areas having air pockets made by the path and the intertwining of the stems.  In the past 80-100 years this view has been challenged by the very realistic concern about how the plant travels as it grows and how intrusive to soft mortar this can be.  The old stems are robust and tree-like.  The young shoots are climbers and they are explorative, using sucking fronds to ‘stick’ to the surfaces they climb.  On an old brick wall with mortar in need of repointing, or with an old sandy mortar, this can lead to young shoots growing into small cavities, fattening as they grow and ultimately breaking up the wall.

Ivy growing on house walls 
Earlier this autumn, I was in Inverness at the time of the Housing Expo.  It was fascinating to see one of the houses employing a mixed innovative and traditional approach.  Scotland, in particular eastern Scotland, can be profoundly affected by strong winds in the winter months.  This house uses a recycled rubber covering to protect the walls from the cooling impact of these winds and ivy is being grown up the side of the building to help with this protection.  It will be very interesting to hear how this and all of the truly innovative houses on this estate fare.  With the rubber coating it will be a while before there will be too many small cavities to be explored.

Aralia hispida in Newfoundland
Finally I am adding a photograph that we used as a Christmas card a few years ago.  It is called Bristly Sarsaparilla and grows on the Avalon Peninsula of Newfoundland.  As a plant it is a distant relative of the American Poison Ivy as well as being a family member of our ivy.  Its form is evocative of the berries and flowers of our own native ivy and several friends were kind enough to remark upon it.  Its latin name is Aralia hispida and Hedera helix is in the Araliaceae family.

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