In The Metamorphoses, plants often function as a way for people to live on after death. Think of Narcissus, who turns into a flower (also called "narcissus"), or Baucis and Philemon, who turn into a pair of trees. (There are many other examples than just these, however.) Maybe part of the reason why plants are such a potent symbol of this is that they grow up out of the ground, where people are buried. In this way, they symbolize rebirth.