Holly – prickly or not
Next time you come across a holly tree, Ilex aquifolium, that is a decent height or girth take a closer look at its leaves.
Holly is a dioecious plant which means that there are male trees and there are female trees. Both produce flowers but only the flowers on the female trees have the ovary necessary for production of red berries. That event of course requires successful pollination of the female flower by a male plant’s pollen. That in turn relies on insects transferring the pollen.
That has nothing to do with the leaves!
However, when you find a suitable holly you should see that some leaves are very spiky yet others are smooth. Spiky leaves will either be on the outside of a good dense tree or in the lower branches of a taller tree. Smooth leaves will be closer to the trunk or higher up respectively.
This is due to the tree being able to modify some of its gene characteristics in response to external pressures. In this case grazing by herbivores.
Leaves that are being exposed to grazing will have the genes switched on that make them spiky when they regrow. The smoother leaves are those out of the reach of grazing animals. Therefore they don’t need to use the energy to produce spikes.
This amazing ability of organisms to switch on or off different traits to adapt to their environment is called epigenetic modification.
The attached photos are of a single tree in the Little Assynt Estate. It’s clear that the smooth leaves are either ‘protected’ by the surrounding prickly leaves or are higher up in the tree.
So, Holly – prickly or not? Both!
David Haines