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Alismatales is an order of flowering plants including about 2500 species. Plants assigned to this order are mostly tropical or aquatic.

Alismatales comprise herbaceous flowering plants of aquatic and marshy habitats, and the only monocots known to have green embryos other than the Amaryllidaceae. They also include the only marine angiosperms.^[1] The flowers are usually arranged in inflorescences, and the mature seeds lack endosperm.

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 aquatic species have a totally submerged juvenile phase, and flowers are either floating or emergent. Vegetation may be totally submersed, hav e floating leaves, or protrude from the water. Collectively they are commonly known as "water plantain".^[2]

Classification

As understood, the order contains about 165 genera in 13 families, with a cosmopolitan distribution.

APG

The Angiosperm Phylogeny Group system (APG) of 1998 and APG II (2003) assigned the Alismatales to the monocots, which may be thought of as an unranked clade containing the families listed below. 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.

• order Alismatales APG-III

The APG III system (2009) differs only in that the Limnocharitaceae are combined with the Al ismataceae; it was also suggested that the genus Maundia (of the Juncaginaceae) could be separated into a monogeneric family, Maundiaceae, but the authors noted that more study was necessary before Maundiaceae could be recognized.

Earlier systems

The Cronquist system (1981) places the Alismatales in subclass Alismatidae, class Liliopsida [= monocotyledons] and includes only three families as shown:

• Alismataceae
• Butomaceae
• Limnocharitaceae

Cronquist's subclass Alismatidae conformed fairly closely to the order Alismatales as defined by APG, minus the Araceae.

The Dahlgren system places the Alismatales in the superorder Alismatanae in the subclass Liliidae [= monocotyledons] in the class Magnoliopsida [= angiosperms] with the following families included:

• Alismataceae
• Aponogetonaceae
• Butomaceae
• Hydrocharitaceae
• Limnocharitaceae

In Tahktajan's classification (1997), the Order Alismatales contains only the Alismataceae and Limnocharitaceae making it equivalent to the Alismataceae as revised in APG-III. Other families included in the Alismatates as currently defined are here distributed among ten additional orders, all of which are assigned, with the following exception, to the Subclass Alismatidae. Araceae in Tahktajan 1997 is assigned to the Arales and placed in the Subclass Aridae; Tofieldiaceae to the Melanthiales and placed in the Liliidae.^[3]

Alismatales comprise herbaceous flowering plants of aquatic and marshy habitats, and the only monocots known to have green embryos other than the Amaryllidaceae. They also include the only marine angiosperms.^[1] The flowers are usually arranged in inflorescences, and the mature seeds lack endosperm.

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 aquatic species have a totally submerged juvenile phase, and 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".^[2]

Classification

As understood, the order contains about 165 genera in 13 families, with a cosmopolitan distribution.

APG

The Angiosperm Phylogeny Group system (APG) of 1998 and APG II (2003) assigned the Alismatales to the monocots, which may be thought of as an unranked clade containing the families listed below. 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.

• order Alismatales APG-III

The APG III system (2009) differs only in that the Limnocharitaceae are combined with the Alismataceae; it was also suggested that the genus Maundia (of the Juncaginaceae) could be separated into a monogeneric family, Maundiaceae, but the authors noted that more study was necessary before Maundiaceae could be recognized.

Earlier systems

The Cronquist system (1981) places the Alismatales in subclass Alismatidae, class Liliopsida [= monocotyledons] and includes only three families as shown:

• Alismataceae
• Butomaceae
• Limnocharitaceae

Cronquist's subclass Alismatidae conformed fairly closely to the order Alismatales as defined by APG, minus the Araceae.

The Dahlgren system places the Alismatales in the superorder Alismatanae in the subclass Liliidae [= monocotyledons] in the class Magnoliopsida [= angiosperms] with the following families included:

• Alismataceae
• Aponogetonaceae
• Butomaceae
• Hydrocharitaceae
• Limnocharitaceae

In Tahktajan's classification (1997), the Order Alismatales contains only the Alismataceae and Limnocharitaceae making it equivalent to the Alismataceae as revised in APG-III. Other families included in the Alismatates as currently defined are here distributed among ten additional orders, all of which are assigned, with the following exception, to the Subclass Alismatidae. Araceae in Tahktajan 1997 is assigned to the Arales and placed in the Subclass Aridae; Tofieldiaceae to the Melanthiales and placed in the Liliidae.^[3]

References

1. ^ -Angiosperm Phylogeny Website
2. ^ -Alismatales (Water Plantains)
3. ^ -Flowering Plant Gateway

• B. C. J. du Mortier 1829. Analyse des Familles de Plantes : avec l'indication des principaux genres qui s'y rattachent. Imprimerie de J. Casterman, Tournay
• W. S. Judd, C. S. Campbell, E. A. Kellogg, P. F. Stevens, M. J. Donoghue, 2002. Plant Systematics: A Phylogenetic Approach, 2nd edition. Sinauer Associates, Sunderland, Massachusetts ISBN 0-87893-403-0.

External links

• NCBI Taxonomy Browser