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Classification System: APG IV

Superregnum: Eukaryota
Regnum: Plantae
Cladus: Angiosperms
Classis: Unassigned
Ordo: Nymphaeales

Familia: Hydatellaceae
Genera: Trithuria

Hydatellaceae U.Hamann New Zealand J. Bot. 14: 195. (1976)

Hamann, U. 1976 New Zealand Journal of Botany 14: 195.
Reveal, J.L. & Doweld, A.B. 1999. Validation of some suprageneric names in Magnoliophyta. Novon 9(4): 549–553. BHL Reference page.
Govaerts, R. et al. 2021. Hydatellaceae in World Checklist of Selected Plant Families. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the internet. Accessed: 2021 June 7. Reference page.
Doweld, A.B. 2001. Prosyllabus Tracheophytorum. Tentamen systematis plantarum vascularium (Tracheophyta) [Prosyllabus Tracheophytorum. Опыт системы сосудистых растений]. LXXX + 110 pp. Moscow: Geos. ISBN 5-89118-283-1. DJVU Reference page.
International Plant Names Index. 2021. 7. Published online. Accessed: June 2021.
Angiosperm 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 Open access Reference page.
Stevens, P.F. 2001 onwards. Angiosperm Phylogeny Website. Version 14, July 2017 [and more or less continuously updated since]. Online. Reference page.
Lohmueller, Friedrich A. The Botanical System of the Plants [1]
Saarela et al., 2007. Hydatellaceae identified as a new branch near the base of the angiosperm phylogenetic tree. Nature 446: 312–5. DOI: 10.1038/nature05612.

Vernacular names
English: Hydatella family
فارسی: خزه‌وشان
한국어: 히다텔라과
മലയാളം: ഹൈഡറ്റലേസീ
polski: Hydatellowate
русский: Гидателловые
slovenčina: Vodniatkovité
中文(简体): 独蕊草科
中文(繁體): 獨蕊草科

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 (order Poales), 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.[3] The family includes only the genus Trithuria, which has at least 13 species, although species diversity in the family has probably been substantially underestimated.[4]


Plants are submerged and emergent aquatic plants, rooted in the substrate below the water. They are tiny plants, just a few cm tall. Most species are ephemeral aquatics that flower in vernal pools when the water draws down, but several species are submerged perennials found in shallow lakes. The simple leaves are concentrated basally around a short stem. Individual species are cosexual (with several types of hermaphroditic conditions) or dioecious, and are either wind-pollinated (anemophilous) or self-pollinating (autogamous). Two predominantly apomictic species are also known.[5] Flower-like reproductive units are composed of small collections of minute stamen- and/or pistil-like structures that may each represent very reduced individual flower, so that the reproductive units may be pseudanthia. The non-fleshy fruits are follicles or achenes.[2]
Trithuria submersa, fruiting

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.[6] 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".[7][8] This realignment is now recognized in the APG III and APG IV systems of classification.[1][9]

The family now includes only the genus Trithuria, which in 2008 was re-defined to include the genus Hydatella.[10]

Angiosperm 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. Archived from the original (PDF) on 25 May 2017. Retrieved 26 June 2013.
Macfarlane, T.D.; Watson, L. & Marchant, N.G., eds. (2000). "Hydatellaceae U Hamann". FloraBase: Flora of Western Australian. Retrieved 15 November 2013.
Givnish, Thomas J.; Zuluaga, Alejandro; Spalink, Daniel; Soto Gomez, Marybel; Lam, Vivienne K. Y.; Saarela, Jeffrey M.; Sass, Chodon; Iles, William J. D.; de Sousa, Danilo José Lima; Leebens-Mack, James; Chris Pires, J.; Zomlefer, Wendy B.; Gandolfo, Maria A.; Davis, Jerrold I.; Stevenson, Dennis W.; dePamphilis, Claude; Specht, Chelsea D.; Graham, Sean W.; Barrett, Craig F.; Ané, Cécile (24 October 2018). "Monocot plastid phylogenomics, timeline, net rates of species diversification, the power of multi-gene analyses, and a functional model for the origin of monocots". American Journal of Botany. Wiley. 105 (11): 1888–1910. doi:10.1002/ajb2.1178. ISSN 0002-9122. PMID 30368769.
Sokoloff, Dmitry D.; Marques, Isabel; Macfarlane, Terry D.; Remizowa, Margarita V.; Lam, Vivienne K.Y.; Pellicer, Jaume; Hidalgo, Oriane; Rudall, Paula J.; Graham, Sean W. (14 April 2019). "Cryptic species in an ancient flowering‐plant lineage (Hydatellaceae, Nymphaeales) revealed by molecular and micromorphological data". Taxon. Wiley. 68: 1–19. doi:10.1002/tax.12026. ISSN 0040-0262.
Smissen, Rob D.; Ford, Kerry A.; Champion, Paul D.; Heenan, Peter B. (2019). "Genetic variation in Trithuria inconspicua and T. filamentosa (Hydatellaceae): a new subspecies and a hypothesis of apomixis arising within a predominantly selfing lineage". Australian Systematic Botany. CSIRO Publishing. doi:10.1071/sb18013. ISSN 1030-1887.
Saarela, Jeffery M.; Rai, Hardeep S.; Doyle, James A.; Endress, Peter K.; Mathews, Sarah; Marchant, Adam D.; Briggs, Barbara G. & Graham, Sean W. (2007). "Hydatellaceae identified as a new branch near the base of the angiosperm phylogenetic tree". Nature. 446 (7133): 312–315. Bibcode:2007Natur.446..312S. doi:10.1038/nature05612. PMID 17361182.
Rudall, Paula J.; Sokoloff, Dmitry D.; Remizowa, Margarita V.; Conran, John G.; Davis, Jerrold I.; Macfarlane, Terry D. & Stevenson, Dennis W. (2007). "Morphology of Hydatellaceae, an anomalous aquatic family recently recognized as an early-divergent angiosperm lineage". American Journal of Botany. 94 (7): 1073–1092. doi:10.3732/ajb.94.7.1073. hdl:2440/44423. PMID 21636477.
Friis, Else Marie; Crane, Peter R. & Pederses, Kaj Raunsgaard (2011). Early Flowers and Angiosperm Evolution. Cambridge University Press. ISBN 978-1-139-12392-1.
Angiosperm Phylogeny Group (2016). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV". Botanical Journal of the Linnean Society. 181 (1): 1–20. doi:10.1111/boj.12385. ISSN 0024-4074.
Sokoloff, Dmitry D.; Remizowa, Terry D. Macfarlane, Paula J. Rudall, Margarita V.; Macfarlane, Terry D. & Rudall, Paula J. (2008). "Classification of the early-divergent angiosperm family Hydatellaceae: one genus instead of two, four new species and sexual dimorphism in dioecious taxa". Taxon. 57: 179–200.

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