Anna, could you post where you were shown the "two types" of Stevia, please?
I've grown it for 14 years now and have only come across, and only researched , Stevia Rebaudiana.
Although for years it was touted hardy to zone 8 it has come back in one of my flower beds for 14 years so feel free to zone push. (But now I notice you are zone 8 so you should be fine.)
The photo you've posted doesn't look like S. rebaudiana; your leaves look too round while S. r. has longer leaves. The flowers of S. rebaudiana also appear at the tops/ends of the branches and in somewhat of a receme fashion. The flowers in your pic, if that is what the white things are, seem to be one flower on an individual petiole.
Lastly, S. rebaudiana is normally propagated best by cuttings as so many of its seeds are normally sterile.
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