Ikebana, the art of arranging flowers, has a long history and has been practised for centuries. First by Buddhist monks living near a lake called Ikenobo, from which the name is derived. 
Apart from flower arrangements for religious rituals, civilians started practising Ikebana as well, which lead to new schools to be established. Nowadays four different schools are known, each with their own rules and specific style. Here are some characteristics:

Ikenobo
Rikka (upright position), Shoka (no supportive materials) & Jiyuka (improv)

Ohara
Moribana (wide and low bowls with landscapes)

Sogetsu
Arrangements with other than organic materials

Ichiyo 
Free-style using seasonal flowers