{{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 that it includes the family Alismataceae. It is a relatively new name: earlier systems, such as the Engler and Wettstein systems, used the name Helobiae for a comparable unit.
==Alismatidae in the Takhtajan system== The Takhtajan system treats this as one of six subclasses within the class Liliopsida (=monocotyledons). It consists of:
* subclass Alismatidae *: superorder Alismatanae *:: order Butomales *:: order Hydrocharitales *:: order Najadales *:: order Alismatales *:: order Aponogetonales *:: order Juncaginales *:: order Potamogetonales *:: order Posidoniales *:: order Cymodoceales *:: order Zosterales
==Alismatidae in the Cronquist system== The Cronquist system treats this as one of four subclasses within the class Liliopsida (=monocotyledons). It consists of (1981):
* subclass Alismatidae *: order Alismatales *: order Hydrocharitales *: order Najadales *: order Triuridales
This subclass comprises less than five hundred species total: many of these are aquatic or semiaquatic plants (see [https://web.archive.org/web/20070927000050/http://www.accessscience.com/Encyclopedia/0/02/Est_022600_frameset.html?doi Alismatidae info]).
==APG II system== The APG II system does not use formal botanical names above the rank of order; it assigns most of the plants involved to the (expanded) order Alismatales, in the clade 'monocots', although the plants in Cronquist's order Triuridales are assigned to quite different placements.
Category:Monocots