The bamboos are a group of woody perennial evergreen (except for certain temperate species) plants in the true grass family. Some are giant bamboos, the largest members of the grass family. Bamboos are the fastest growing woody plants in the world. Their growth rate (up to 60 centimeters (24 in.)/day) is due to a unique rhizome-dependent system, but is highly dependent on local soil and climate conditions. They are of economic and high cultural significance in East Asia and South East Asia where they are used extensively in gardens, as a building material, and as a food source. There are more than 70 genera divided into about 1,000 species. They are found in diverse climates, from cold mountains to hot tropical regions.