Like animals, plants evolve by adapting to their surroundings.
Lancewood Vs. Moa
For example, New Zealand's lancewood tree has evolved to defend itself against being eaten by the moa--a large, flightless bird related to the emu and ostrich.
Scientists speculate that as a tiny seedling, the lancewood grows small brown leaves that help the infant tree blend in with leaf litter on the forest floor. So a prowling moa might pass by and spare the plant.
As it grows, the lancewood's leaves change, becoming long and spiky, with barbs along the edges. Scientists believe that bright spots near the barbs are probably meant to get moas' attention and make them think twice about trying to swallow such a prickly meal.
Finally, when they reach adulthood, the lancewood's leaves change once again, becoming rounder and losing their spikes. Why? Perhaps because the tree is now tall enough to hoist its leaves out of the reach of hungry moas.
Still A Threat?
Now, what's especially interesting about all this is that while the lancewood tree still thrives in New Zealand, moas were hunted to extinction around five-hundred years ago. But the trees they once dined upon still go about their business as though the birds were still a threat.
What It All Means
First, that scientists can really only speculate about why the lancewood behaves the way it does. But it also suggests that to really understand a plant's evolution, we have to consider not only its current environment but also its past. Defenses evolved against now-extinct predators may still shape a plant's appearance and behavior today.