Mutation for thick stems and large leaves in Supertunia?

Hello!

I purchased this Supertunia Giant Pink from a local garden center, specifically because it was so much larger than the others. These leaves are approximately twice the size of the other Supertunias present.

I'm trying to make sense of what I'm looking at.

Is this a mutation that occurred when this stem was first growing? Is it confined to this stem? There is new growth at the base that is much closer to what I'd expect to find in a petunia, underneath these massive leaves.

The larger growth is *ridiculously* fragile. I broke multile midribs getting it home and taking pictures. I haven't really tested the smaller growth at the base, as doing so risks breaking more leaves.

I haven't yet seen a flower, but the petals already seem thicker than the other petunias i have on the patio.