KISS OF THE PARASITE SPREADING THROUGH GLASNEVIN

Diarmuid Breatnach

(Reading time: 3 mins.)

At this time of year, using a parasitic plant as an excuse — and in spite of Covid19 transmission danger — many kisses will be given. The plant in question is of course the mistletoe and people buy sprigs or clumps of it to hang in strategic places to trap the unwary, ambushing them into receiving the sign of affection (or lust). Although the plant is native across Europe it is not so to Ireland1, though it can be found growing in widely-separated places here, believed to be the result of “garden escapes” but could also have been imported with saplings (for example of apple varieties).

IN FOLKLORE AND MYTHOLOGY

According to Wikipedia, the whole kissing-under-mistletoes custom was popularised by courting couples among servants of middle and upper classes during the reign of the English Queen Victoria. How that arose is not explained but there has been an association of the berries with fertility since antiquity, possibly through sympathetic magic, since the berries were thought to resemble sperm. Indeed, one of its medicinal uses historically has been in treatment of infertility, along with arthritis, high blood pressure and epilepsy. To the Celts, mistletoe represented the semen of Taranis, their god of thunder2, while the Ancient Greeks referred to mistletoe as “oak sperm”.

Closeup of Viscum album, the north European mistletoe, leaves and white berries.
(Photo sourced: Internet)

Modern medicine does not ascribe scientific value to treatments with misteltoe and instead points to the toxicity of the plants, with Tyramine, the active agent, causing blurred vision, diarrhoea, nausea and vomiting and, more rarely, seizures, hypertension and even cardiac arrest. The toxic agent is maximally concentrated in the fruits and leaves. Fatalities among adult humans are rare but children and pets are more vulnerable.

Mistletoe on tree in January 2017, Dublin area (possibly Botanic Gardens). (Photo: D.Breatnach)

In Ancient Rome it was customary to attach a sprig of the plant above the door to bring love and peace to the household while elsewhere it has also been seen as protection against evil spirits. What of the common belief that it was ingested by the druids, as in a “ceremony of the oak and mistletoe” with sacrifice of white bulls? We have only Pliny as an ancient source of that alleged ceremony and historians seem to dislike relying on him, seeing him as a historian who liked to please the patricians in Rome with his descriptions. Wiki comments: “Evidence taken from bog bodies makes the Celtic use of mistletoe seem medicinal rather than ritual. It is possible that mistletoe was originally associated with human sacrifice and only became associated with the white bull after the Romans banned individual human sacrifices.”3

Is mistletoe harmful to trees? Although it is not in the long-term interests of a parasite to kill its host, some species do appear to be taking over their host bush or tree but we don’t seem to have come to that pass in Ireland and indeed may never do so. Wikipedia notes a number of studies that have ascribed ecological importance to some species, as a food source, nesting material and even encouraging the spread of juniper through birds attending parasitised juniper trees and eating the mistletoe and juniper berries together, to pass through the gut unharmed and be deposited elsewhere.4

THE PLANT SPREADING IN IRELAND?

“The word ‘mistletoe’ derives from the older form ‘mistle’ adding the Old English word tān (twig). ‘Mistle’ is common Germanic (Old High German mistil, Middle High German mistel, Old English mistel, Old Norse mistil). Further etymology is uncertain, but may be related to the Germanic base for ‘mash’.”5 Its family Solanthacea (agreed in 2003) includes about 1,000 species in 43 genera. Many have reported traditional and cultural uses, including as medicine.6

Clumps of Drualus (mistletoe) on unidentified tree, Botanic Gardens, Dublin, October 2020. (Photo: D.Breatnach)

In Ireland, apart from its scientific name Viscum alba, the perennial plant has a number of names: Sú Dara, Uile Íce, Drua-Lus and it typically roots itself in the bark of trees such as Hawthorn, Lime, Apple, Poplar and Willow but according to its Wikipedia entry, “successfully parasitizes more than 200 tree and shrub species” (though probably much less in Ireland). Once established its roots tap its host’s sap for water and nutrients but it also carries out photosynthesis, processing sunshine through its fleshy leaves — which has it classified as a hemiparasite, ie. it does part of its own work. The tree also gives it elevation where it can catch the sun’s rays without too much obstruction.

A distribution map with the Wildflowers of Ireland entry shows it widespread throughout England and Wales and localised in Scotland and Ireland, possibly through the deforestation in those nations. Although imported deliberately or accidentally to Ireland and then escaping beyond its source, once established it can be be spread, largely probably by birds.

Smólach Mór (Mistle Thrush), Griffiths Park, Glasnevin-Drumcondra, June 2021. (Photo: D.Breatnach)

The Mistle Thrush (Smólach Mór/ Turdus viscivorus) is particularly associated with the plant by name and the bird is said to include the berries in its winter diet when invertebrate animals, its preferred food the rest of the year, are rarely about7. The bird is described as squeezing the berries in its beak, ejecting the seeds sideways and, to clean its beak, wiping it against a tree trunk. The seeds, being covered with sticky liquid adhere to the tree bark and the liquid hardens, maintaining a strong grip.

Clumps of Irish mistletoe on a north American Poplar, Botanic Gardens, Dublin, 19th December 2021. (Photo: D.Breatnach)
Nameplate on the bark of the poplar tree parasitised by the mistletoe picture above. (Photo: D.Breatnach)

The parasitic plant has long been in evidence in the National Botanic Gardens in Dublin and to a lesser extent in the adjacent Glasnevin Cemetery and I wondered at times why it (along with the grey squirrels) did not make its way into Griffiths Park, only minutes away on foot and connected by the Tolka River. However, walking through that park the other day, I did indeed spy the tell-tale clump high up in a tree.

One of two clumps of mistletoe on a poplar tree in Griffiths Park in January 2022 (Photo: D.Breatnach)

So it is spreading.

End.

Footnotes

1According to the Wildflowers of Ireland website.

2From Proto-Celtic Toranos (note “torann”, Irish for “noise” and the word “tone” in English).

3While having humans killed in the arena in large-scale displays for mass entertainment!

4One of the many methods of seed dispersal and why plants produce seeds inside edible packages such as fruit.

5Wikipedia

6Ibid

7While the Wikipedia entry on the bird states that it eats mistletoe berries along with those of ivy and yew (all poisonous to humans), the Birdwatch Ireland web page states only that it eats berries in winter, without specifying which ones.

References

https://en.wikipedia.org/wiki/Mistletoe

http://www.wildflowersofireland.net/plant_detail.php?id_flower=641&wildflower=Mistletoe

Mistle Thrush

https://en.wikipedia.org/wiki/Mistle_thrush

1According to the Wildflowers of Ireland website.

2From Proto-Celtic Toranos (note “torann”, Irish for “noise” and the word “tone” in English).

3While having humans killed in the arena in large-scale displays for mass entertainment!

4One of the many methods of seed dispersal and why plants produce seeds inside edible packages such as fruit.

5Wikipedia

6Ibid

7While the Wikipedia entry on the bird states that it eats mistletoe berries along with those of ivy and yew (all poisonous to humans), the Birdwatch Ireland web page states only that it eats berries in winter, without specifying which ones.