Tidbit from Agriculture Canada

Stevia rebaudiana Bertoni is one of 154 members of the genus Stevia. It is a member of the Compositae family and as such is related to sunflower, marigolds etc. Stevia has an alternate leaf arrangement and herbacious growth habit with flowers arranged in indeterminate heads. The flowers are small and white with a pale purple throat. The pollen can be highly allergenic. Stevia is self-incompatible and probably insect pollinated, the seeds are small, have very little endosperm and are dispersed in the wind via a hairy pappus.