page_title: Hydatellaceae
section_title: Taxonomy
hierarchical_section_title: Hydatellaceae / Taxonomy
caption_attribution_description: Fruiting Trithuria submersa, Tasmannia
context_page_description: Hydatellaceae are a family of small, aquatic flowering plants. The family consists of tiny, relatively simple, plants occurring in Australasia and India. It was formerly considered to be related to the grasses and sedges, but has been reassigned to the order Nymphaeales as a result of DNA and morphological analyses showing that it represents one of the earliest groups to split off in flowering-plant phylogeny, rather than having a close relationship to monocots, which it bears a superficial resemblance to due to convergent evolution. The family includes only the genus Trithuria, which has at least 13 species, although species diversity in the family has probably been substantially underestimated.
context_section_description: The family was for many years assumed to be a close relative of the grasses and sedges and was even sometimes lumped under the poalean family Centrolepidaceae. Even as recently as 2003, the APG II system assigned Hydatellaceae to the grass order Poales in the commelinid monocots. However, research based on DNA sequences and morphology by Saarela et al. indicates that Hydatellaceae is the living sister group of the water lilies (Nymphaeaceae and Cabombaceae) and thus represents one of the most ancient lineages of flowering plants. Developers of earlier classifications were misled by the apparently reduced vegetative and reproductive morphology of these plants. As aquatic herbs, Hydatellaceae have environmental adaptations leading to derived characteristics that create a morphological similarity to the more distant taxon. Careful reanalysis of their morphological traits and comparisons with other so-called 'basal' angiosperms have supported this "dramatic taxonomic adjustment". This realignment is now recognized in the APG III and APG IV systems of classification.
  The family now includes only the genus Trithuria, which in 2008 was re-defined to include the genus Hydatella.
caption: Trithuria submersa, fruiting
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