What do you mean by "largely unchanged"? One notable recent example is wheat. The University of Houston's College of Engineering has done extensive research into evolution of wheat. They have found that up to 10,000 years ago (circa 8000 BC) the ancestor of wheat more closely resembled a wild grass than the heavy grain-bearing plant we eat today. Then a mutation occurred in which this plant was crossed with another grass. The result was a fertile hybrid called emmer with edible seeds that blew in the wind and sowed themselves.
Then a second genetic mutation occurred sometime between 8000 and 6000 B.C. This mutation yielded something very close to our modern wheat, with its much plumper grain.
Same with corn.