Pandanales (pandans or screw-pines) is the botanical name for an order of flowering plants placed in the monocot clade in the Angiosperm Phylogeny Group and Angiosperm Phylogeny Web systems. Within the monocots Pandanales are grouped in the lilioid monocots where they are in a sister group relationship with the Dioscoreales. Historically the order has consisted of a number of different families in different systems but modern classification of the order is based primarily on molecular phylogenetics despite diverse morphology which previously placed many of the families in other groupings based on apparent similarity. Members of the order have a subtropical distribution and includes palms, trees, shrubs, and vines as well as herbaceous plants. The order consists of 5 families, 36 genera and about 1,610 species.
Pandanales are highly diverse including large arboraceous plants of tropical rainforests and coastal areas, climbing vines and lianas, as well as very small achlorophyllous (mycoheterotrophic) and saprophytic herbaceous forest floor species. This has made it difficult to reliably define synapomorphies, but the loss of trimery distinguishes many of them from other lilioid monocots.
The Pandanales order is distinctive with its highly variable and hardly definable floral morphology, especially the number of stamens and their structure so as many other characteristics. In some of the members, even different interpretations exist about the composition and organization of the reproductive structures. The structure of the inflorescence also varies.
The order includes plants with traits that seem atypical when compared to other groups of monocots. A good example is the female reproductive organ and its position relative to other parts of the flower. Some of the species included in the families Pandanaceae and Stemonaceae show flowers formed from only one carpel, while in the Triuridaceae, a family that lacks chlorophyll, the carpels are free from each other. In fact, the Triuridaceae hold the most doubtful flower morphology from the whole order.