According to scientific definitions, bamboo is grass, but in terms of legislation, it is often classified as a tree. As a perennial evergreen grass in the family Poaceae (Gramineae), bamboo belongs to the subfamily Bambusoideae. Of all grasses, bamboo is the largest and the only one that can diversify into a forest. While bamboo is a grass, many of the larger woody bamboo species resemble trees and are often called "bamboo trees".