If you are asking why sending flowers of artificially propagated plants is permitted and on the other hand sending flowers of wild plants is not, then I guess it is because: If you cut off the gonads of the wild growing plants, then they cannot propagate in the wild anymore.
You're right Amar, it's late
That's not my question... I don't understand why FLOWERS of artificially propagated plants is permitted while sending artificially propagated plants NOT. I guess it is for a reason of pests, disease or insects, but in my opinion what we can find on a plant, we can also find on a flower. Or not? (for example aphids or red spiders too, they are really small).