Polyploid Stevia?

At a few local garden centers, I have come across Stevia plants that appear to be two to three times larger than normal Stevia in every respect. The leaves measure 2" long by 1" wide, and the green, growing stems are as big around as a pencil. However, on one plant, it appeared that a few stems had reverted back to the "normal" dimensions I am used to seeing. Is it possible that these plants are artificially-induced polyploids? If so, have you heard of this before?

We are not aware of any polyploids or special cultivars that differ morphologically compared to what has been sold on the North American market over the past decade. Seed-grown stevia always starts out with larger leaves compared to material grown from cuttings; however, over time the seed grown material will eventually revert to the narrower leaf form.
We have not seen the stem thickness you describe even in the juvenile seed-grown material so we cannot say that the plants you describe completely fit what we know stevia to be.