Sweetleaf (Stevia Rebaudiana)
This is a NON-artificial sweetener. Very, very sweet, so use less. It said to be 10-300 times sweeter than sucrose (white table sugar). Note that it has been used for centuries...
http://mikesbackyardnursery.com/2015/03/how-to-grow-a-stevia-plant/Stevia is an perennial, not noted for producing a lot of viable seeds, but you can do cuttings to propagate new plants.
You can buy a starter planet (Stevia Rebaudiana ONLY) from some nurseries or you may be able to get a cutting from friends.
If trimmed to prevent blossoming, the plant will continue to produce leaves (which you harvest).
Aside: I do this to Sweet Basil. I have about five plants in a very small pot, which get cut back to leave two growth rings, which then produce new branches on a six week cycle.