The Alismatales (alismatids) are an order of

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

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

tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

aquatic Aquatic means relating to water; living in or near water or taking place in water; does not include groundwater, as "aquatic" implies an environment where plants and animals live. Aquatic(s) may also refer to: * Aquatic animal, either vertebrate ...

. Some grow in

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salt (chemistry), salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include ...

, some in

marine habitats A marine habitat is a habitat that supports 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 environmen ...

. Perhaps the most important food crop in the order is the

taro Taro (; ''Colocasia esculenta'') is a root vegetable. It is the most widely cultivated species of several plants in the family Araceae that are used as vegetables for their corms, leaves, stems and Petiole (botany), petioles. Taro corms are a ...

plant, ''Colocasia esculenta''.

Description

The Alismatales comprise

herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition of ...

flowering plants of often aquatic and marshy habitats, and the only monocots known to have green

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

s other than the

Amaryllidaceae The Amaryllidaceae are a family of herbaceous, mainly perennial and bulbous (rarely rhizomatous) flowering plants in the monocot order Asparagales. The family takes its name from the genus '' Amaryllis'' and is commonly known as the amaryl ...

. They also include the only marine angiosperms growing completely submerged, the

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

es. The

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

s are usually arranged in

inflorescence In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a mai ...

s, and the mature seeds lack

endosperm The endosperm is a tissue produced inside the seeds of most of the flowering plants following double fertilization. It is triploid (meaning three chromosome sets per nucleus) in most species, which may be auxin-driven. It surrounds the Embryo#Pla ...

. 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 emerge above the water's surface. 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 In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

Phylogenetically In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

, 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) is a clade of flowering plants within the monocots, distinguished by having cell walls containing ferulic acid. Well-known commelinids include palms and relatives (order Arecales), day ...

monocot Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are flowering plants whose seeds contain only one Embryo#Plant embryos, embryonic leaf, or cotyledon. A monocot taxon has been in use for several decades, but ...

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 oldes ...

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

Early systems

The

Cronquist system The Cronquist system is a list of systems of plant taxonomy, taxonomic classification system of angiosperms, flowering plants. It was developed by Arthur Cronquist in a series of monographs and texts, including ''The Evolution and Classification of ...

(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 20 genera (17 extant and 3 fossil) and 119 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 plant ...

Limnocharitaceae Limnocharitaceae was a family of flowering plants in the monocot order Alismatales.Robert R. Haynes, Donald H. Les, and Lauritz B. Holm-Nielsen. 1998. "Limnocharitaceae". pages 271-275. In: Klaus Kubitzki (general editor) with Klaus Kubitzki, Herb ...

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 198 ...

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 Ta ...

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 classi ...

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 which includes 14 accepted genera and a total of ca 135 known species (Christenhusz & Byng 2016). The family holds a number of species of aquatic plants, including tape-grass, the well-known Canadian ...

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 In the classifica ...

and placed in the Subclass Aridae; Tofieldiaceae to the

Melanthiales Melanthiales Johann Heinrich Friedrich Link, Link (melanthoid lilies) was an Order (biology), order of monocotyledons, whose name and botanical authority is derived by typification from the description of the Type (biology), type Family (biology), ...

and placed in the

Angiosperm Phylogeny Group

The Angiosperm Phylogeny Group system (

APG APG may refer to: * Aberdeen Proving Ground, a United States Army installation in Aberdeen, Maryland **Phillips Army Airfield (IATA code), the airfield of the above * Aboriginal Provisional Government, Indigenous Australian independence movement * ...

) 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 Gro ...

(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 The APG III system of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy being developed by the Angiosperm Phylogeny Group (APG). Published in 2009, it was superseded in 2016 by a f ...

(2009) differs only in that the

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 ''Maundia '' is a genus of alismatid monocots, described in 1858. ''Maundia'' was formerly included in the family Juncaginaceae but is now considered to form a family of its own under the name Maundiaceae. It contains only one known species, ''M ...

, 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 co ...

'' APG III *: family

(''including''

) *: 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). Also ...

*: 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 ...

*: 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 ...

*: 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 five genera. The largest genus in the family by far is '' Potamogeton'', ...

*: family

Ruppiaceae ''Ruppia'', also known as the widgeonweeds, ditch grasses or widgeon grass, is the only extant genus in the family Ruppiaceae, with 11 known species. These are aquatic plants widespread over much of the world. The genus name honours Heinrich Be ...

*: family

Scheuchzeriaceae ''Scheuchzeria palustris'' (Rannoch-rush, or pod grass), is a flowering plant in the family Scheuchzeriaceae, in which there is only one species and ''Scheuchzeria'' is the only genus. In the APG II system it is placed in the order Alismatales of ...

*: family

Tofieldiaceae Tofieldiaceae is a family of flowering plants in the monocot order Alismatales.Vernon H. Heywood, Richard K. Brummitt, Ole Seberg, and Alastair Culham. ''Flowering Plant Families of the World''. Firefly Books: Ontario, Canada. (2007). . The famil ...

*: 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 published ...

(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 "unispe ...

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''

) *: family

*: family

Phylogeny

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

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). Ter ...

'' 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