TheAlismatales (alismatids) are an order offlowering plants including about 4,500 species. Plants assigned to this order are mostlytropical oraquatic. Some grow infresh water, some inmarine habitats. Perhaps the most important food crop in the order is thetaro plant,Colocasia esculenta.
The Alismatales compriseherbaceous flowering plants of often aquatic and marshy habitats, and the only monocots known to have greenembryos other than theAmaryllidaceae. They also include the only marine angiosperms growing completely submerged, theseagrasses.[2] Theflowers are usually arranged ininflorescences, and the mature seeds lackendosperm.
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.[3] 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".[4]
TheCronquist system (1981) places the Alismatales in subclassAlismatidae, classLiliopsida [= 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.
TheDahlgren system places the Alismatales in the superorderAlismatanae in the subclassLiliidae [= monocotyledons] in the classMagnoliopsida [= 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 theArales and placed in the Subclass Aridae; Tofieldiaceae to theMelanthiales and placed in theLiliidae.[7]
The Angiosperm Phylogeny Group system (APG) of 1998 andAPG 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 fromearlier 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.[8]
TheAPG III system (2009) differs only in that theLimnocharitaceae are combined with the Alismataceae; it was also suggested that the genusMaundia (of theJuncaginaceae) could be separated into a monogeneric family, theMaundiaceae, but the authors noted that more study was necessary before the Maundiaceae could be recognized.[1]
InAPG IV (2016), it was decided that evidence was sufficient to elevateMaundia to family level as themonogeneric Maundiaceae.[8] 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.[9] Consequently, the family structure for APG IV is:
^abAngiosperm 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,hdl:10654/18083
B. C. J. du Mortier 1829. Analyse des Familles de Plantes : avec l'indication des principaux genres qui s'y rattachent. Imprimerie de J. Casterman, Tournay
W. S. Judd, C. S. Campbell, E. A. Kellogg, P. F. Stevens, M. J. Donoghue, 2002. Plant Systematics: A Phylogenetic Approach, 2nd edition. Sinauer Associates, Sunderland, MassachusettsISBN0-87893-403-0.
