A subclass of the monocotyledons containing both herbaceous and arborescent (the palms) plants. Members of the Arecidae differ from other monocotyledons in having broad net-veined petiolate leaves. Their numerous small flowers are usually unisexual and grouped into an inflorescence subtended by a spathe. Four orders are commonly recognized: the Arecales, which contains one family, the Arecaceae or *Palmae
(palms); the Cyclanthales, which also contains one family, the Cyclanthaceae; the Arales, which contains the two families Lemnaceae (which includes the duckweeds), and Araceae (which includes the arums or aroids); and the Pandanales, which comprises the one family Pandanaceae (which includes the screw pines). In some classifications the order Typhales is placed in the Arecidae, while in others it is allocated to the Commelinidae. The Typhales includes two families, the monotypic Typhaceae, containing the cattails and reedmace bulrush (Typhus), and the monotypic Sparganiaceae, containing the bur-reeds (Sparganum).