Land will be trees, beaches will be crabs, and I've heard oceans will be nothing but jellyfish

That makes sense. And I feel like it makes me understand trees better. This is what I’m thinking.

The fitness landscape for a moving creature underwater is pretty limited. You gotta be hydrodynamic and there aren’t many solutions to that. But we still get variety; eels and jellyfish, for example.

With plants you also have some strong limitations. Plants don’t move. They’re rooted to the ground. Plus they compete over height. So, the solution set consists of sturdy and tall trees.

Moving creatures on land have a lot of more options so evolution achieved more variety. I’m not sure if distinct branches of moving creatures on land arrived at the “same” evolutionary solution.