The bamboos /bæmˈbuː/ (listen) are evergreen perennial flowering plants in the subfamily Bambusoideae of the grass family Poaceae. The word "bamboo" comes from the Dutch or Portuguese languages, which probably borrowed it from Malay. In bamboo, as in other grasses, 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. Bamboos include some of the fastest-growing plants in the world, due to a unique rhizome-dependent system. Certain species of bamboo can grow 910 mm (36 in) within a 24-hour period, at a rate of almost 40 mm (1.6 in) an hour (a growth around 1 mm every 90 seconds, or 1 inch every 40 minutes). Giant bamboos are the largest members of the grass family.