Studies of European mistletoe’s host preferences often show distinct preferences for particular varieties, or cultivars, within a tree species – so that some varieties of Apple tree are more susceptible than others, as are some varieties of Lime tree, Poplar tree etc.
Demonstrating this convincingly on the ground is difficult – as you generally need a lot of data for lots of trees.
But on Christmas Day this year I suddenly found the perfect demo virtually on our doorstep! And wondered why I’d never noticed it before…
Some background: We live on the edge of Stonehouse, not far from the old Standish Hospital, a rural former NHS hospital now standing empty and decaying in its own grounds – which are a mini-arboretum, with many splendid exotic mature trees. The driveway up to the site has an avenue of relatively young (maybe 30-40 years old) ornamental maples.
Now, we’ve been here over 14 years now, and have walked that drive regularly, as there’s a bridleway route though the site. And over those years we’ve watched as mistletoe has established in those maples, colonising from existing mistletoe colonies in the remnant apple orchards nearby (there’s an old orchard at both ends of the drive) and from mistletoe in nearby poplars.
The revelation: The mistletoe in the maples is now fairly well established – and on Christmas Day afternoon, as we wandered up the hospital drive and back in an effort to walk off some lunch, I was idly assessing the mistletoe in each tree (as one does) – and suddenly realised that… every other tree in each side of the avenue was mistletoe-free. And the mistletoe-free trees were never opposite across the avenue either. So, if plotted on a map the mistletoe trees would be a zig zag pattern along the drive.
And why would that be? Well, these maple trees are two varieties – one a red-leaved one and one a green-leaved one – and they are planted in an alternating pattern. So… the mistletoe, which we’ve witnessed developing over the last 14 years, is only colonising one of the maple varieties – not the other. Which one? Well I think it is the red-leaved one – but will have to wait until spring for confirmation. The aerial photo on the right, when compared to the mistletoe pattern we’ve seen (we checked it again today), seems to confirm red though.
So, there you have it – mistletoe colonising one variety of a tree but not another closely related one – despite having decades to do it in and the trees being right next to each other. I’m just slightly embarrassed that I’ve only just noticed!
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