Why Do Plants Keep Evolving Into Trees?

What makes a tree a tree has nothing to do with height — and a palm tree fails the test. The film cuts inside oaks, palms, bananas, bamboo and dragon trees to reveal the vascular cambium and true wood. It traces arborescence as convergent evolution over 320 million years, from 40-meter Carboniferous club mosses held up by bark to tree ferns wrapped in roots, and why island herbs are still evolving into trees today.