I am trying to remember the name of a sci-fi book written by a female. The book starts out with a husband trying to kill a weed, to no avail. In time, his wife leaves him and befriends the weed. Eventually the weed helps her arrive at time in the future where people are being ridden by animals. I have been trying to figure this out for years! Thanks to anyone who can help.By the way I read it in the late 90's and in English.