Ikebana is known as the art of Japanese flower arranging. But it is directly translated as the arrangement of plant materials, meaning the artist is not 
limited only to the showy and colorful blooms of traditional Western florists. Ikebana began as ancient monks offered flowers at temples, in much the same way that bonsai developed as a discipline. We now recognize the minimalist style and its influences everywhere. The arrangements express poetry, emotion, and aesthetic appreciation. And they are also meant to mirror natural ways, where symmetry and perfect balance are eschewed.
Many rules govern the true schools of Ikebana, including dictating the height of the stems, the types of containers, and even the angles at which stems can be placed. This is because Ikebana is a discipline, historically practiced by the samurai. It is my belief that these rules are important, but do not let them intimidate you. The benefits of working with plants and flowers can still be had for the novice. Flowers will always enhance the home, and with Ikebana, they enhance your artistic soul.
Source
http://blog.craftzine.com