The bamboos are a group of woody perennial evergreen (except for certain temperate species) plants in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. 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.