Selection is the opposite of random.
that which survives and that which dies sometimes has nothing to do with anything other than pure chance.
Sometimes. But sometimes not.
We're going through evolutionary pressures right now because of (sun caused) global warming. I live on the edge of a tree micro climate, and that edge is creeping to a point where I expect this house will be in a field in 50 years.
Granted, this property will likely be populated with existing species. But the *individual* plants will die out, and be replaced by others because of natural selection by climate.
If we had only a field grass, but no trees, there would be a condition that favored the evolution of trees, and no doubt it would happen in a few million years. This is how selection aids evolution.
Climate is only one method of selection. It can be sexual selection, cultural, predation, many things. Those are the details of evolution still being worked out.
prove it
The problem is that the selections you've mentioned have had nothing to do with the genetic code of the plants that you've mentioned.
A tree is still a tree. Johnson grass is still Johnson grass. Etc.