Is there anything as romantic as kissing under a parasitic poisonous plant?
Servant classes in Victorian Britain are said to have popularised mistletoe's link with kissing. A man was allowed to kiss any woman who stood under the mistletoe, and if she refused, this would bring her bad luck. One custom decreed that a berry must be pulled from the mistletoe after each kiss, and the kissing had to end when there were no berries left
For me, mistletoe conjures up scenes from old Christmas movies or that song about 'Mommy kissing Santa Claus'. We never hung mistletoe in our house growing up — not because we were anti-kissing, but probably because it’s not a native Irish plant, so I doubt there was any available to buy back then.
This was a time when Christmas decorations amounted to a straggly tree and perhaps some tinsel sellotaped to the ceiling.
Of course, mistletoe has great cultural significance, but its biology is fascinating. The European Mistletoe — the familiar ‘Christmas variety’ — belongs to a large group of obligate hemi-parasitic plants, meaning they live on another ‘host’ plant, from which they extract most of their nutrients and water.
The ‘obligate’ bit means they cannot survive independently without their host. The European mistletoe, Viscum album, looks like a dense ball of twigs and leaves high up on the branch of a tree and can easily be mistaken for a crow’s large nest.
It is attached by a structure it forms — the haustorium — through which it extracts what it needs from its host.
In the past, gardeners have tried to grow mistletoe in Ireland, but it hasn’t spread successfully and the distribution map on the National Biodiversity Data Centre’s website shows just a small number of records. In winter, you might mistake a ‘witch’s broom’ (commonly seen in Irish trees) for mistletoe, but this is actually an irregular growth of the tree’s own tissue, as opposed to a parasite.
How does the mistletoe get up into the tree canopy?
Mistletoe berries are popular with birds, who spread its seeds. Indeed the Mistle Thrush owes its name to this plant. Birds eat the white fruits and the seeds are either regurgitated or excreted, but they can also stick to the bird’s bill.
Because evolution is so amazing, the seeds are covered in ‘viscin’ — a sticky material which adheres to the bird's beak until the bird, probably annoyed by its presence, wipes it away on the nearest branch. And hey presto, the seed has found its new home, or should we say the parasite its new host!
Once it touches the host’s branch or bark, the viscin hardens and bonds the seed to the tree, where it can germinate and its haustorium invade the host plant.
There are more than 1,000 mistletoe species, growing in every continent except Antarctica. Mistletoe species are called ‘hemiparasites’ as opposed to full parasites because they do carry out a little photosynthesis themselves, at some stage in their life cycle.
Although having said that, some species have all but given up contributing anything to their own sustenance.
Some mistletoe species grow almost entirely inside their host plant, with only their fruit and flowers emerging to betray their hiding place, such as the Chilean Tristerix aphyllus, which lives deep inside a spiny cactus.
It’s only when its red flower emerges from the cactus that you would know it was there, living inside.
Early Celtic pagans were probably the first to associate mistletoe with this time of year.
At the winter solstice, any evergreen plants were held in high esteem as they had refused to be defeated by the cruelty of winter. Because the female mistletoe produces white berries in mid-winter, this would have also drawn attention to the plant.
The Romans associated mistletoe with love and peace and began to hang it from doorways to protect the household. By the 18th century, mistletoe had been adopted into Christmas traditions in many parts of the world.
Servant classes in Victorian Britain are said to have popularised the link with kissing. A man was allowed to kiss any woman who stood under the mistletoe, and if she refused, this would bring her bad luck.
One custom decreed that a berry must be pulled from the mistletoe after each kiss, and the kissing had to end when there were no berries left.
Mistletoe is poisonous, but toxicity to humans varies widely depending on the species. Eating the leaves or berries could cause vomiting, diarrhoea, blurred vision, and cardiac problems. And, of course, risks are much more serious in small children than in adults.
But if you find yourself standing under some mistletoe at the same time as someone you fancy this holiday season, it's safe to pucker up.
- Juanita Browne has written a number of wildlife books, including and .
