Alismatales is an order of flowering plants.
Alismatales comprise flowering plants of aquatic and marshy habitats, and the only monocots known to have green embryos other than the Aarillidaceae. They also include the only marine angiosperms. Both marine and freshwater forms include those with staminate flowers that detach from the parent plant and float to the surface where they become pollinated. In others, pollination occurs underwater where pollen may form elongated strands, increasing chance of success. Most species have a totally submerged juvenile phase. Flowers are either floating or emergent. Vegetation may be totally submersed, have floating leaves, or protrude from the water. Collectively they are commonly known as "water plantain".
The Alismales were assigned in APG 1998 and APG-II 2003 to the Monocotyledonae (class Liliopsida Tahktajan), which may be thought of as an unranked clade, with the following families included. APG-3 (2009) differs only in that the Limnocharitaceae are combined with the Alismataceae and genus Maundia was separated from Juncaginaceae to establish family Maundiaceae.
As understood, the order contains about 165 genera in 14 families, with a cosmopolitan distribution. Most of the families are composed of herbaceous plants, commonly found in aquatic environments. The flowers are usually arranged in inflorescences, and the mature seeds lack endosperm.
The biggest departure from earlier systems (see below) is the inclusion of family Araceae. By its inclusion the order has grown enormously in number of species. The family Araceae alone accounts for about a hundred genera, totaling over two thousand species. The rest of the families together contain only about five hundred species.
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