Which came first, the plant or the seed?

I was thinking of a phrase people often get wrong. Which is you reap what you sow. Too often I hear people say it in reverse. But the truth is that the seeds you grow will produce seeds that can be weak and produce a bad crop.
Its kind of like, what came first, the chicken or the egg?
So it got me wondering. How is it possible we have so many variations of plants that produce seeds? I saw a documentary one day that showed a desert valley come to life with hundreds of variations of plants after a few seasons of rain. They figured seeds where in hibernation until the rain came back to the desert.