The Poaceae (English pronunciation: /poʊˈeɪ.siˌiː/) or Gramineae are the large and nearly ubiquitous family of monocotyledonous flowering plants known as grasses. The Poaceae include the cereal grasses, bamboos and the grasses of natural grassland and cultivated lawns (turf) and pasture. Grasses have stems that are hollow except at the nodes and narrow alternate leaves borne in two ranks. The lower part of each leaf encloses the stem, forming a leaf-sheath. With ca 780 genera and around 12,000 species, Poaceae are the fifth-largest plant family, following the Asteraceae, Orchidaceae, Fabaceae and Rubiaceae.