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Alismatales

(Order)

Overview

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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.

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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

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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.

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:

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

[ Back to top ]

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

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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.

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:

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 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

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

External links

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Photos

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Taxonomy

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The Order Alismatales is further organized into finer groupings including:

Families

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Acoraceae

[more]

Alismataceae

Herbs, annual or perennial, rhizomatous, stoloniferous, or cormose, caulescent, glabrous to stellate-pubescent; sap milky. Roots septate or not septate. Leaves basal, submersed, floating, or emersed, sessile or petiolate, sheathing proximally; blade with translucent markings of dots or lines present or absent, basal lobes present or absent; venation reticulate, primary veins parallel from base of blade to apex, secondary veins reticulate. Inflorescences scapose racemes or panicles, rarely umbels, erect, rarely floating or decumbent, whorled (forming racemes) or whorls branching (forming panicles), bracteolate. Flowers bisexual or unisexual, if unisexual, staminate and pistillate on same or different plants, hypogynous, subsessile to long-pedicellate; sepals persistent, 3; petals deciduous, 3, delicate; stamens 0, 6, 9, or to 30, distinct; anthers 2-loculed, dehiscing longitudinally; pistils 0 or 6--1500 or more, distinct or coherent proximally, 1-loculed; placentation basal; ovules1--2. Fruits achenes or follicles. Seeds: embryo U-shaped; endosperm absent in mature seed.[1] [more]

Aponogetonaceae

The Aponogetonaceae (Cape-pondweed family or Aponogeton family) are a family of flowering plants in the order Alismatales. [more]

Araceae

Herbs, perennial, wetland or terrestrial, occasionally emergent or floating, [often epiphytic or climbing], usually with milky or watery latex, rarely colored. Rhizomes, corms, or stolons present; rhizomes vertical or horizontal, creeping at or near surface, sometimes branched; corms underground, starchy; stolons at or near surface. Stems absent [sometimes aboveground or aerial]. Cataphylls usually present. Leaves rarely solitary, alternate or clustered; petiole rarely absent, with sheathing base; blade simple or compound [occasionally perforate], elliptic to obovate or spatulate, occasionally sagittate-cordate, larger than 1.5 cm; venation parallel or pinnate- or palmate-netted. Inflorescences spadices, each with 3--900 usually tightly grouped, sessile flowers, subtended by spathe; spathe rarely absent, persistent (sometimes only proximally) or deciduous, variously colored; spadix cylindric or ovoid, various parts occasionally naked or with sterile flowers. Flowers bisexual or unisexual, staminate and pistillate usually on same plants or functionally on different plants, staminate flowers distal to pistillate when unisexual; perianth absent or present; stamens 2--12, distinct or connate in synandria; ovaryies 1, 1--3(--many) -locular, sessile or embedded in spadix; styles 1; stigmas hemispheric, capitate, or discoid [sometimes strongly lobed]. Fruits berries, distinct or connate at maturity. Seeds 1--40(--many) per berry.[2] [more]

Butomaceae

Herbs, perennial, rhizomatous, stemless, glabrous; sap clear. Roots not septate. Leaves basal, emersed or rarely submersed, sessile, sheathing somewhat proximally; blade with lade: translucent markings absent, basal lobes absent; venation parallel. Inflorescences scapose umbels, erect, bracteate. Flowers bisexual, hypogynous, pedicellate; tepals persistent, 6, in 2 series, scarious; stamens 9, distinct; anthers 4-loculed, dehiscing longitudinally; pistils 6, coherent proximally, 1-loculed; placentation laminar; ovules 50. Fruits follicles. Seeds: embryo straight; endosperm absent in mature seed.[3] [more]

Cymodoceaceae

Herbs, perennial, rhizomatous, caulescent; turions absent. Leaves submersed, alternate or nearly opposite, sessile; sheath persisting longer than blade, leaving circular scar when shed, not ligulate, auriculate, lobes not scarious; blade linear; intravaginal squamules scales, more than 2. Inflorescences axillary or terminal, solitary or cymes, without spathe, sessile or pedunculate; peduncle, when present, not elongating following fertilization, not spiraling. Flowers uniasexual, staminate and pistillate on separate plants; subtending bracts absent; perianth absent. Staminate flowers: stamens 2, in 1 series; anthers adaxially connate, dehiscing vertically; pollen linear. Pistillate flowers: pistils 2, distinct, not stipitate; ovules pendulous, orthotropous. Fruits achenelike or drupaceous. Seeds 1; embryo straight.[4] [more]

Hydrocharitaceae

[more]

Juncaginaceae

Herbs, perennial or annual, rhizomatous, evident stems absent; turions absent. Leaves basal, emersed, sessile; sheath persisting longer than blade, not leaving circular scar when shed, ligulate, auriculate with scarious lobes; blade linear; intravaginal squamules scales, more than 2. Inflorescences terminal or axillary, scapose spikes, spikelike racemes, rarely solitary flowers, without spathe, pedunculate; peduncle following fertilization not elongating, not spiraling. Flowers bisexual or unisexual, staminate and pistillate on same plant; subtending bracts absent; perianth present, rarely absent; tepals 1, or 6 in 1--2 series. Bisexual and staminate flowers: stamens 1, 4, or 6, epitepalous, when 4 or 6, then in 2--3 series; anthers distinct, dehiscing longitudinally; pollen globose. Pistillate and bisexual flowers: pistils 1, 3, or 6, not stipitate, when 3 or 6, coherent or weakly connate; ovules basal, anatropous. Fruits nutlets or schizocarps. Seeds 1; embryo straight.[5] [more]

Limnocharitaceae

Herbs, perennial, rhizomatous or stoloniferous, caulescent, glabrous; sap milky. Roots not septate. Leaves basal [alternate], submersed and floating [emersed], sessile or petiolate, sheathing proximally; blade with translucent markings absent, basal lobes absent; venation reticulate, primary veins parallel from base of blade to apex, secondary veins reticulate. Inflorescences scapose umbels, floating [erect], bracteate. Flowers bisexual, hypogynous, pedicellate; sepals persistent, 3; petals deciduous, 3, usually delicate; stamens [6--]20--25, distinct; anthers 4-loculed, dehiscing longitudinally; pistils [3--]10--12, coherent proximally [distinct], 1-loculed; placentation laminar; ovules 50 or more. Fruits follicles. Seeds: embryo U-shaped; endosperm absent in mature seed.[6] [more]

Posidoniaceae

Posidonia is a genus of flowering plants. It contains two to nine species of marine plants ("seagrass"), found in the seas of the Mediterranean and around the south coast of Australia. [more]

Potamogetonaceae

Herbs, perennial or rarely annual, rhizomatous or not rhizomatous, caulescent; turions absent or present. Leaves alternate or nearly opposite, submersed or both submersed and floating, sessile or petiolate; sheath not persisting longer than blade, not leaving circular scar when shed, ligulate, not auriculate, or rarely auriculate; intravaginal squamules scales, more than 2. Inflorescences terminal or axillary, spikes, capitate spikes, or panicles of spikes, not subtended by spathe, pedunculate; peduncle not elongating, not spiraling following fertilization. Flowers bisexual; subtending bracts absent; tepals 4 in 1 series; stamens [2 or] 4, epitepalous, in 1 series; anthers distinct, dehiscing vertically; pollen spheric; pistils 1 or 4, mostly not stipitate, rarely short-stipitate; ovules marginal, orthotropous. Fruits drupaceous. Seeds 1; embryo curved.[7] [more]

Ruppiaceae

Herbs, annual or rarely perennial, not rhizomatous, caulescent; turions absent [present]. Leaves alternate to subopposite, submersed, sessile; sheath not persisting longer than blade, not leaving circular scar when shed, not ligulate, not auriculate; blade linear; intravaginal squamules scales, 2. Inflorescences terminal, capitate spikes, with subtending spathe, pedunculate; peduncle following fertilization often elongating, often spiraling. Flowers bisexual; subtending bracts absent; perianth absent; stamens 2, in 1 series; anthers distinct, dehiscing longitudinally; pollen arcuate; pistils 4--16, distinct, stipitate; ovules parietal, campylotropous. Fruits drupaceous. Seeds 1; embryo straight.[8] [more]

Scheuchzeriaceae

Herbs, perennial, rhizomatous, caulescent; turions absent. Leaves alternate, emergent, sessile; sheath with remains often persisting, auriculate; blade linear, nearly cylindric, with conspicuous round pore adaxially on leaf tip; intravaginal squamules hairs, numerous. Inflorescences terminal, bracteate racemes, not subtended by spathe; pedicels following fertilization elongating, not spiraling. Flowers bisexual; subtending bracts present; perianth present; tepals 6; stamens 6, epitepalous; anthers basifixed, distinct, dehiscing longitudinally, extrorse; pollen globose; pistils 3(--6), distinct to slightly connate at base; ovules basal-marginal, anatropous. Fruits follicles. Seeds 1--2(--3) .[9] [more]

Tofieldiaceae

[more]

Zosteraceae

Herbs, perennial, rarely annual, rhizomatous, caulescent; turions absent. Leaves alternate, submersed, sessile; sheath persisting longer than blade or decaying with age into bundles of woolly fibers, not leaving circular scar when shed, not ligulate, auriculate with scarious lobes; blade linear; intravaginal squamules scales, more than 2. Inflorescences axillary or terminal, spadices, surrounded by spathe, pedunculate; peduncle following fertilization not elongating, not spiraling. Flowers unisexual, staminate and pistillate on same plant or different plants; subtending bracts (retinacula) often present; perianth absent. Staminate flowers: stamens 1; anthers dehiscing longitudinally; pollen linear. Pistillate flowers: pistils1, not stipitate; ovules pendulous, orthotropous. Fruits achenelike. Seeds 1; embryo straight.[10] [more]

At least 76 species and subspecies belong to the Family Zosteraceae.

More info about the Family Zosteraceae may be found here.

References

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

External links

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Bibliography

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Footnotes

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  1. Robert R. Haynes ,C. Barre Hellquist "Alismataceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org.
  2. Sue A. Thompson "Araceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org.
  3. Robert R. Haynes "Butomaceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org.
  4. Robert R. Haynes "Cymodoceaceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org.
  5. Robert R. Haynes, C. Barre Hellquist "Juncaginaceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org.
  6. Robert R. Haynes "Limnocharitaceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org.
  7. Robert R. Haynes ,C. Barre Hellquist "Potamogetonaceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org.
  8. Robert R. Haynes "Ruppiaceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org.
  9. Mark A. Nienaber "Scheuchzeriaceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org.
  10. Robert R. Haynes "Zosteraceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org.

Sources

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Last Revised: February 23, 2012
2012/02/23 15:08:51