044 Dracunculus vulgaris at Akrotiri peninsula, Crete, Greece

The Alismatales (alismatids) are an order of

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

s including about 4,500 species. Plants assigned to this order are mostly

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

or aquatic. Some grow in fresh water, some in

marine habitats Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea (the term ''marine'' comes from the Latin ''mare'', meaning sea or ocean). A habitat is an ecological or environmental ...

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

seagrass Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the or ...

es. The

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...

s are usually arranged in

inflorescence An inflorescence is a group or cluster of flowers arranged on a Plant stem, stem that is composed of a main branch or a complicated arrangement of branches. Morphology (biology), Morphologically, it is the modified part of the shoot of sperma ...

s, 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. There they can pollinate carpellate flowers floating on the surface via long pedicels. 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".

Taxonomy

The Alismatales contain about 165 genera in 13 families, with a cosmopolitan distribution. Phylogenetically, they are

basal monocot In phylogenetics, basal is the direction of the ''base'' (or root) of a rooted phylogenetic tree or cladogram. The term may be more strictly applied only to nodes adjacent to the root, or more loosely applied to nodes regarded as being close to th ...

s, diverging early in evolution relative to the

lilioid Lilioid monocots (lilioids, liliid monocots, petaloid monocots, petaloid lilioid monocots) is an informal name used for a grade (grouping of taxa with common characteristics) of five monocot orders (Petrosaviales, Dioscoreales, Pandanales, Lil ...

and

commelinid In plant taxonomy, commelinids (originally commelinoids) (plural, not capitalised) is a clade of flowering plants within the monocots, distinguished by having cell walls containing ferulic acid. The commelinids are the only clade that the APG IV ...

monocot Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one Embryo#Plant embryos, embryonic leaf, or cotyledon. Th ...

lineages. Together with the

Acorales ''Acorus'' is a genus of monocot flowering plants. This genus was once placed within the family Araceae (aroids), but more recent classifications place it in its own family Acoraceae and order Acorales, of which it is the sole genus of the old ...

, the Alismatales are referred to informally as the alismatid monocots.

Early systems

The

Cronquist system The Cronquist system is a taxonomic classification system of flowering plants. It was developed by Arthur Cronquist in a series of monographs and texts, including ''The Evolution and Classification of Flowering Plants'' (1968; 2nd edition, 1988) ...

(1981) places the Alismatales in subclass

Alismatidae {{Short description, Subclass of flowering plants Alismatidae is a botanical name at the rank of subclass. Circumscription of the subclass will vary with the taxonomic system being used (there are many such systems); the only requirement being t ...

, class

Liliopsida Liliopsida Batsch (synonym: Liliatae) is a botanical name for the class containing the family Liliaceae (or Lily Family). It is considered synonymous (or nearly synonymous) with the name monocotyledon. Publication of the name is credited to Scopol ...

monocotyledonsand includes only three families as shown: *

Alismataceae The water-plantains (Alismataceae) are a family of flowering plants, comprising 19 genera (17 extant and 2 fossil) and 117 species. The family has a cosmopolitan distribution, with the greatest number of species in temperate regions of the Northe ...

Butomaceae ''Butomus'' is the only known genus in the plant family Butomaceae, native to Europe and Asia. It is considered invasive in some parts of the United States. Taxonomy The Butomaceae family has been recognized by most taxonomists as a pla ...

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

Dahlgren system One of the modern systems of plant taxonomy, the Dahlgren system was published by monocot specialist Rolf Dahlgren in 1975 and revised in 1977, and 1980. However, he is best known for his two treatises on monocotyledons in 1982 and revised in 19 ...

places the Alismatales in the superorder Alismatanae in the subclass

Liliidae Liliidae is a botanical name at the rank of subclass. Circumscription of the subclass will vary with the taxonomic system being used (there are many such systems); the only requirement being that it includes the family Liliaceae. Liliidae in T ...

monocotyledonsin the class

Magnoliopsida Magnoliopsida is a valid botanical name for a class of flowering plants. By definition the class will include the family Magnoliaceae, but its circumscription can otherwise vary, being more inclusive or less inclusive depending upon the classif ...

angiospermswith the following families included: *

Aponogetonaceae The Aponogetonaceae (the Cape-pondweed family or aponogeton family) are a family of flowering plants in the order Alismatales. In recent decades the family has had universal recognition by taxonomists. The APG system (1998) and APG II system (20 ...

Hydrocharitaceae Hydrocharitaceae is a flowering plant family including 16 known genera with a total of ca 135 known species (Christenhusz & Byng 2016), that including a number of species of aquatic plant, for instance the tape-grasses, the well known Canadian ...

* 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 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 ''Arales'' is an order of flowering plants. The name was used in the Cronquist system for an order placed in subclass ''Arecidae'', circumscribed as (1981): * order ''Arales'' *: family '' Acoraceae'' *: family ''Araceae'' *: family ''Lemnaceae' ...

and placed in the Subclass Aridae; Tofieldiaceae to the

Melanthiales Melanthiales Link (melanthoid lilies) was an order of monocotyledons, whose name and botanical authority is derived by typification from the description of the type family, Melanthiaceae by Johann Heinrich Friedrich Link in 1829. In Rolf Dahlgr ...

and placed in the

Angiosperm Phylogeny Group

The Angiosperm Phylogeny Group system ( APG) of 1998 and

APG II The APG II system (Angiosperm Phylogeny Group II system) of plant classification is the second, now obsolete, version of a modern, mostly molecular-based, system of plant taxonomy that was published in April 2003 by the Angiosperm Phylogeny Gr ...

(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. 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 Juncaginaceae is a family of flowering plants, recognized by most taxonomists for the past few decades. It is also known as the ''arrowgrass'' family. It includes 3 genera with a total of 34 known species (Christenhusz & Byng 2016 ). The APG II ...

) could be separated into a monogeneric family, the Maundiaceae, but the authors noted that more study was necessary before the Maundiaceae could be recognized. * order Alismatales ''

sensu ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...

'' APG III *: family

(''including'' Limnocharitaceae) *: family

*: family

Araceae The Araceae are a family of monocotyledonous flowering plants in which flowers are borne on a type of inflorescence called a spadix. The spadix is usually accompanied by, and sometimes partially enclosed in, a spathe (or leaf-like bract). A ...

*: family

Cymodoceaceae Cymodoceaceae is a family of flowering plants, sometimes known as the "manatee-grass family", which includes only marine species. The 2016 APG IV does recognize Cymodoceaceae and places it in the order Alismatales, in the clade monocots. The fam ...

*: family

Posidoniaceae ''Posidonia'' is a genus of flowering plants. It contains nine species of marine plants ("seagrass"), found in the seas of the Mediterranean and around the south coast of Australia. The APG system (1998) and APG II system (2003) accept this gen ...

*: family

Potamogetonaceae The Potamogetonaceae, commonly referred to as the pondweed family, is an aquatic family of monocotyledonous flowering plants. The roughly 110 known species are divided over six genera. The largest genus in the family by far is ''Potamogeton'', w ...

*: family

Ruppiaceae ''Ruppia'', also known as the widgeonweeds, ditch grasses or widgeon grass, is the only extant genus in the family Ruppiaceae, with eight known species. These are aquatic plants widespread over much of the world. The genus name honours Heinrich ...

*: family Scheuchzeriaceae *: family Tofieldiaceae *: family

Zosteraceae Zosteraceae (one of the four seagrasses families, Kubitzki ed. 1998) is a family of marine perennial flowering plants found in temperate and subtropical coastal waters, with the highest diversity located around Korea and Japan. Most seagrasses ...

APG IV The APG IV system of flowering plant classification is the fourth version of a modern, mostly molecular-based, system of plant taxonomy for flowering plants (angiosperms) being developed by the Angiosperm Phylogeny Group (APG). It was publishe ...

(2016), it was decided that evidence was sufficient to elevate ''Maundia'' to family level as the

monogeneric In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

Maundiaceae. 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. Consequently, the family structure for APG IV is: *: family

(''including'' Limnocharitaceae) *: family

*: family

*: family Maundiaceae *: family

*: family

*: family Scheuchzeriaceae *: family Tofieldiaceae *: family

Phylogeny

Cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

showing the orders of monocots (

Lilianae Lilianae (also known as Liliiflorae) is a botanical name for a superorder (that is, a rank higher than that of order) of flowering plants. Such a superorder of necessity includes the type family Liliaceae (and usually the type order Liliales). Te ...

'' Chase & Reveal) based on molecular phylogenetic evidence:

References

External links

* * {{Authority control Angiosperm orders

Description

Taxonomy

Early systems

Angiosperm Phylogeny Group

Phylogeny

References

Further reading

External links