The bamboos /bæmˈbuː/ are a subfamily (Bambusoideae) of flowering perennial evergreen plants in the grass family Poaceae. Giant bamboos are the largest members of the grass family. In bamboo, the internodal regions of the stem are usually hollow and the vascular bundles in the cross section are scattered throughout the stem instead of in a cylindrical arrangement. The dicotyledonous woody xylem is also absent. The absence of secondary growth wood causes the stems of monocots, including the palms and large bamboos, to be columnar rather than tapering.