There's a staggering lot we don't know about plants. It's partly due to their nightmarish genome complexity (often polyploid), their slow generation time (taking often decades to mature and reproduce) and the impossibility to reproduce the complex micro-organism communities found in the soil in which they thrive.

Much of the cool stuff we know (such as e.g. transmitting responses to stress to other individuals) we've only learned a couple years ago. This is truly an exciting time to make discoveries.