An order of monocotyledons, the composition of which only recently has been revealed by deoxyribonucleic acid (DNA) sequence studies of four genes. Included are four families, two of which have been generally viewed as closely related: Pandanaceae (800 species; the screw pine family) and Cyclanthaceae (230 species; the Panama hat family). These two families have often been considered to be related to Arecales (with a single family, Arecaceae, palms), but actually the relationship is distant. In addition, the order includes Stemonaceae (35 species) and Velloziaceae (200 species), which have been thought to be related to Dioscoreaceae (Dioscoreales) and Bromeliaceae (Commelinales) or Hypoxidaceae (Asparagales), respectively. Pandanaceae are often lianas or large herbs from the Old World; Cyclanthaceae are herbs or lianas from the New World tropics; Stemonaceae are herbs or lianas of the Old World (but with one species in the southeastern United States); and Velloziaceae are herbs or small shrubs of Africa and particularly South America (with one genus in southwest China). Cyclanthaceae, Pandanaceae, and Stemonaceae have flower parts in twos or fours, which is unusual among monocotyledons, in which threes are most common.