What does Hawthorne say the rose symbolizes?

How about this,

He speculates that the rosebush might have sprung up from the footsteps of Ann Hutchinson - a woman persecuted, like Hester will be. He does directly tell us, however, in the final line of the chapter that the rose symbolizes a "sweet moral blossom" to "relieve the darkening close of a tale of human frailty and sorrow." In other words, the narrator tells us that the rose will symbolize a lesson to be learned in the midst of this tragic tale.

The rose represents the blossoming of good from darkness.