Question

the characteristics of body design used for classification of plants will be different from those important for classifying animals. why

Answer 1

This is because of the presence of certain parts in plants that differ in function when compared to their metazoan counter parts, Yes I am Talking about the apical meristems these are the parts of plants which are analogous to stem cells present in animals but they can give rise to functional plant organ i.e. Stem root leaf etcetera unlike the Animals which have the body plans designed at the time of embryo development.
Once the embryo starts developing the body plan gets fixed as the axis gets determined and all the cells are committed to give rise to a specific body part.
moreover there is involvem of several Morphogens (factors determining the morphology) in the development.
these are the things why Animal and Plant body designs are distinct from each other.