Ikebana is the Japanese art of flower arrangement, also known as kadÅ, which means "way of flowers". The tradition dates back to the Heian period, when floral offerings were made at altars, and later, flower arrangements were used to adorn the tokonoma of a traditional Japanese room. Ikebana is a disciplined art form in which nature and humanity are brought together, and it is more than simply putting flowers in a container. The key features of ikebana include emphasizing other areas of the plant, such as its stems and leaves, and putting emphasis on shape, line, and form. Ikebana has evolved over the centuries, and today there are many different styles of arrangement, such as the heika style, which includes rikka (standing flowers), shoka (living flowers), and seika (flung flowers), and the moribana (piled-up flowers) style when using dish-like containers called suiban. Ikebana is a visual art that uses plant materials that come in a wide variety of forms, and artistic judgment must be used to readjust the established forms. The philosophy behind ikebana is grounded in Japanese aesthetics, which emphasizes simplicity, understated elegance, and a respect for nature. Ikebana can be practiced by both amateurs and professionals, and it takes several years to acquire the technical and expressive skills necessary to arrange the stems and flowers exactly as one wishes.