Alismatales

The Alismatales (alismatids) are an order of flowering plants including about 4500 species. Plants assigned to this order are mostly tropical or aquatic. Some grow in fresh water, some in marine habitats.

Alismatales
Alisma plantago-aquatica
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Alismatales
R.Br. ex Bercht. & J.Presl[1]
Families

See Classification

Snake lily (Dracunculus vulgaris) of family Araceae in Crete, Greece.
Ottelia alismoides from family Hydrocharitaceae in Hyderabad, India.

Description

The Alismatales comprise herbaceous flowering plants of often aquatic and marshy habitats, and the only monocots known to have green embryos other than the Amaryllidaceae. They also include the only marine angiosperms growing completely submerged, the seagrasses.[2] 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".[3]

Taxonomy

The Alismatales contain about 165 genera in 13 families, with a cosmopolitan distribution. Phylogenetically, they are basal monocots, diverging early in evolution relative to the lilioid and commelinid monocot lineages.[4] Together with the Acorales, the Alismatales are referred to informally as the alismatid monocots.[5]

Early systems

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

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:

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 10 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.[6]

Angiosperm Phylogeny Group

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, many of which are in very small families.[7]

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, the Maundiaceae, but the authors noted that more study was necessary before the Maundiaceae could be recognized.[1]

In APG IV (2016), it was decided that evidence was sufficient to elevate Maundia to family level as the monogeneric Maundiaceae.[7] The authors considered including a number of the smaller orders within the Juncaginaceae, but an online survey of botanists and other users found little support for this "lumping" approach.[8] Consequently, the family structure for APG IV is:

Cladogram of Alismatales[2]
Alismatales
 

Tofieldiaceae

 
 
 
 
 

Alismataceae

 
 
 

Butomaceae

 
 

Hydrocharitaceae

 
 
 
 
 

Aponogetonaceae

 
 
 

Scheuchzeriaceae

 
 
 

Juncaginaceae

 
 
 

Maundiaceae

 
 
 
 

Posidoniaceae

 
 
 

Ruppiaceae

 
 

Cymodoceaceae

 
 
 
 
 

Potamogetonaceae

 
 

Zosteraceae

 
 
 
 
 
 
 
 
 

Araceae

 
 
 

Phylogeny

Cladogram showing the orders of monocots (Lilianae sensu Chase & Reveal)[9] based on molecular phylogenetic evidence:

Lilianae sensu Chase & Reveal[9]
 
 

Acorales

 
 
 

Alismatales

 
 
 

Petrosaviales

 
 
 
 

Dioscoreales

 
 

Pandanales

 
 
 
 

Liliales

 
 
 

Asparagales

 
commelinids
 

Dasypogonaceae

 
 

Arecales

 
 

Poales

 
 
 

Zingiberales

 
 

Commelinales

 
 
 
 
 
 
 
 
 
 
Alismatid monocots

References
  1. Angiosperm Phylogeny Group (2009), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III", Botanical Journal of the Linnean Society, 161 (2): 105–121, doi:10.1111/j.1095-8339.2009.00996.x
  2. Stevens, P.F. (2001). "Alismatales". Angiosperm Phylogeny Website. 14. Missouri Botanical Garden. Retrieved 14 March 2018.
  3. "-Alismatales (Water Plantains)" (PDF). Archived from the original (PDF) on 12 June 2010. Retrieved 27 May 2010.
  4. Wilkin & Mayo 2013.
  5. RBG 2010.
  6. -Flowering Plant Gateway
  7. APG IV 2016.
  8. Christenhusz et al. (2015)
  9. Chase & Reveal 2009.

Further reading
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