Publication Type:Book Chapter
Year of Publication:1995
Authors:Les, D. H., Haynes R. R.
Editor:Cutler, D. F., Humphries C. J.
Book Title:Monocotyledons: systematics and evolution
Publisher:Royal Botanic Gardens Kew

The study of systematic relationships in and of the monocotyledon subclass Alismatidae has incorporated comparative methods, phenetic approaches and cladistic analyses. Characters used in these analyses have included morphological, anatomical, ultrastructural, biochemical and molecular data. We review the bases and limitations of different hypotheses for relationships of the subclass to other angiosperms, and for interfamilial relationships within the group. Although cladistic analyses have provided many insights to phylogenetic relationships of Alismatidae, the homology of morphological character states in this mainly aquatic group is frequently uncertain and subject to alternative interpretations. One result is that cladistic analyses using morphological features provide equal support for considerably different hypotheses of relationships in Alismatidae. The incorporation of molecular data in cladistic analyses is a potentially powerful technique to study phylogenetic relationships of aquatic plants characterised by highly homoplasious morphological features. Former and current systematic studies consistently indicate strong support for the monophyly of subclass Alismatidae. Relationships within the subclass are less certain, although there is now much evidence to indicate a close phylogenetic relationship between the families Hydrocharitaceae and Najadaceae, and the distinctness of Ruppiaceae and Potamogetonaceae.

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