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 ...

or aquatic. 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. 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 monocots, diverging early in evolution relative to the lilioid 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, class Liliopsida 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 * 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 monocotyledonsin the class Magnoliopsida angiospermswith the following families included: *

* 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 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 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 Liliidae.

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. 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 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. * 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'' Limnocharitaceae) *: family Aponogetonaceae *: 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 Butomaceae *: 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 Hydrocharitaceae *: family Juncaginaceae *: family Posidoniaceae *: family Potamogetonaceae *: family Ruppiaceae *: family Scheuchzeriaceae *: family Tofieldiaceae *: family Zosteraceae In APG IV (2016), it was decided that evidence was sufficient to elevate ''Maundia'' to family level as the monogeneric 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 Aponogetonaceae *: family

*: family Butomaceae *: family

*: family Hydrocharitaceae *: family Juncaginaceae *: family Maundiaceae *: family Posidoniaceae *: family Potamogetonaceae *: family Ruppiaceae *: family Scheuchzeriaceae *: family Tofieldiaceae *: family Zosteraceae

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 ''

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

References

External links

* * {{Authority control Angiosperm orders