Green Leaves & Tops of Plants: It's Where the Nutrients Are.

Taken from Chapter 5 "Why Is It Hard to Love Greens?" of Victoria Boutenko's Green for Life 

Green leaves were never included into our food pyramids as a separate group because humans never looked at them as real food.  Carrot tops have several times more nutrition than the roots, but the opinion that greens are for rabbits, sheep, and cows, has been preventing us from eating carrot tops in our salads.  We routinely throw away the most nutritious part of the carrot plant!  The roots are much more palatable to human taste than the tops because the roots contain significantly more sugar and water.  The tops are bitter from the abundant amount of nutrients in them.