The flowers are grouped by color, an easy and natural approach, but not very scientific. For example, the flower Monks Hood appears in two places, it is both a blue and a white flower. As well, Colorado Columbine is classified as a blue flower, although it has almost as much white as blue. A flower that I call red, my wife may call pink. The non-flowering plants are grouped by broad simplistic classifications easy for us laymen to follow.