Natural Variation in Rose or Swamp Milkweed

I noticed last year that the rose or swamp milkweed (Asclepias incarnata) I planted had significant natural variation in the leaves. The photo below shows three different plants – note the variation in color and size as well as the shape, size and texture of the leaves:

The plant to the left has fuzzy rounded leaves:

The middle plant has longer, paler and less fuzzy leaves:

And the right-most plant has long and narrow leaves that are not at all fuzzy. It also is significantly taller than the other two plants, and has not yet begun to bud:

I find the natural variation fascinating and would love to learn more about it. For example, if I knew more about botany would I know that one of these plants would be better adapted to drier soil based on its characteristics?