Along with the holly and the ivy, mistletoe is one of those species which is intimately associated with the festive season. You might almost say it is a hemi-parasite on the cultural Christmas tree…
A small group of us undertook some voluntary tree climb surveys in Clumber Park before Christmas 2018 to look for roosting bats. One of the trees which I climbed was an old lime set amongst younger trees and this had some beautiful examples of mistletoe right in the top of the crown. It seemed a good opportunity to share some photos and ecological insights into this fascinating plant.
Mistletoe is a obligate hemi-parasite – it is only found growing attached to trees. This is because it is partially reliant on the tree for sustenance – it taps into the xylem system of the tree to source water and soil minerals. It does however phytosynthesise itself which makes it only a half or partial (hemi) rather than full parasite.
Mistletoe does not have roots, rather it grows on the surface of the branch and encourages the tree to grow around it. This gives the illusion of it penetrating the bark to reach into the branch and take its sustenance, but the truth is much less aggressive.
The main ‘mistletoe’ heartland in the UK is the south-west midlands – this is particularly around Herefordshire, Somerset, Monmouthshire and Gloucestershire and up as far as Warwickshire. It is however found sporadically in many other locations around the country – close to Grantham, the village of Bottesford seems to be unusually well covered. The origins of these more isolated pockets of mistletoe is often unclear, but many old parklands and country estates tried to establish colonies in the past and it may be that these give rise to local populations away from their stronghold. Given the history of Clumber, this might be a good explanation for the colony I found!
Mistletoe expresses a significant preference for some tree species over others – cultivated apple is the most well-recorded host with lime (like the Clumber tree) coming in second. Other species include hawthorn, poplar, maple, and willow. They have however been recorded on hundreds of tree hosts and some have particular cultural significance – mistletoe growing on oak was the centrepiece of a Celtic religious ceremony.
Most fruit and berry-bearing species in the UK owe a debt to wild birds who disperse the seeds, but mistletoe has a particular reliance upon them. Some species, such as the aptly named mistle thrush, will eat the seeds and excrete them again – often whilst perched on a branch. Not only does this deliver the berries right to the branches but it comes with its own ‘glue’ in the form of the droppings, to help hold the seed in place whilst they develop. Other species such as blackcap wipe the seeds from their beak directly onto the tree – a cleaning action which is coincidentally very likely to deliver the seed to an ideal spot for germination.
This means of spreading seed is the reason for the common name of mistletoe – ‘mistle’ derives from the Anglo-Saxon word for dung and ‘tan’ derives from the word for twigs. The latin is Viscum album – the album meaning ‘white’ and relating to the colour of the berries.
Small patches of mistletoe often go un-noticed or overlooked – either because it is concealed by the dense leaf cover of its host tree, or because people are simply not looking up and around to spot it. Winter is an ideal time to spot this fascinating species – keep your eyes skywards and look out for the characteristic globes of vegetation suspended bauble-like in the branches!
If you want to find out more about mistletoe – its ecology, natural history, cultural significance, distribution and commercial importance – I would highly recommend reading Jonathan Briggs’ Mistletoe Diary blog!