Did you know that holly leaves can actually change shape to ward off hungry herbivores like deer? It’s true! Holly (Ilex aquifolium) has a secret weapon against nibblers: its leaves can transform based on how much danger they’re in.

On the lower branches, where deer and other animals are more likely to munch, the holly produces sharp, spiny leaves that are about as friendly to chew on as a mouthful of needles. These spiky leaves make it difficult—and painful—for animals to take a bite, giving the holly an effective way to protect itself. But higher up, where there’s less risk, the leaves are much smoother and spine-free.

Holly's ability to change its leaf shape to produce spiny or smooth leaves based on environmental threats is an example of epigenetics in action! Epigenetics refers to changes in gene expression that don’t involve altering the underlying DNA sequence but are instead triggered by environmental factors. In the case of holly, the plant seems to "sense" herbivore pressure—like deer browsing—and responds by activating genes that produce spiny leaves in vulnerable areas, such as lower branches.

What makes this even more fascinating is that these changes can be rapid and reversible, meaning that the same tree can have both smooth and spiny leaves depending on where the leaves grow and the level of threat they face. This adaptability is a great example of how epigenetics allows plants to respond to their environment in ways that help them survive.