Hydatellaceae

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Hydatellaceae

Scientific classification

Kingdom:	Plantae
Division:	Magnoliophyta
Class:	Magnoliopsida
Family:	Hydatellaceae U.Hamann (1976)

Genera

Hydatella
Trithuria

Hydatellaceae is the botanical name for a family of flowering plants containing the genera Hydatella and Trithuria. These small, relatively simple, aquatic plants are found only in Australasia and India. The simple leaves are concentrated around a short stem basally. The plants are submerged and emergent aquatic annuals, rooted in the substrate below the water. The members of this plant family are monoecious and are hydrophilous or autogamous. Flowers are clustered into spikelets. The non-fleshy fruits are follicles or achenes.^[1]

Hydatellaceae was for many years assumed to be close relatives of the grasses and sedges and were often included in the family Centrolepidaceae. However, research by Saarela et al. indicates that the Hydatellaceae is the living sister group of the water lilies (Nymphaeales) and thus represent one of the most ancient lineages of flowering plants.^[2] This realignment represents the first time a plant family has been ejected from the monocots.^[3]

The APG II system, of 2003 (unchanged from the APG system, 1998), recognizes a separate family Hydatellaceae and assigns it to the order Poales in the clade commelinids, in the monocots. The family consists of probably fewer than a dozen species. The Cronquist system, of 1981, also recognised such a family and placed it in its own order Hydatellales, in the subclass Commelinidae in class Liliopsida [=monocotyledons]. Both of these taxonomic systems have not been updated to incorporate the information from the 2007 study that removed Hydatellaceae from the monocots. The Angiosperm Phylogeny Website, however, has now placed Hydatellaceae in the order Nymphaeales,^[4] a classification that was not reported in Saarela et al., which suggested instead a sister-group relationship between Nymphaeales and Hydatellaceae.^[2]

[edit] References

^ T.D. Macfarlane, L. Watson and N.G. Marchant (Editors) (2000 onwards). Western Australian Genera and Families of Flowering Plants. Western Australian Herbarium. Version: August 2002. FloraBase: Hydatellaceae. Accessed 20 March 2007.
^ ^a ^b Saarela, Jeffery M., Hardeep S. Rai, James A. Doyle, Peter K. Endress, Sarah Mathews, Adam D. Marchant, Barbara G. Briggs & Sean W. Graham. 2007. Hydatellaceae identified as a new branch near the base of the angiosperm phylogenetic tree. Nature 446:312-315.
^ Graham, S. A New Understanding of the Early Evolution of Flowering Plants. University of British Columbia Botanical Garden press release, 14 March 2007.
^ Stevens, P. F. (2001 onwards). Nymphaeales. Angiosperm Phylogeny Website. Version 7, May 2006. Accessed 21 March 2007.