Trithuria is a genus of small ephemeral aquatic herb that represent the only members of the family Hydatellaceae found in India, Australia, and New Zealand.Kew World Checklist of Selected Plant Families Almost all described species of Trithuria are found in Australia, with the exception of T. inconspicua and T. konkanensis, from New Zealand and India respectively.Dmitry D. Sokoloff, Margarita V. Remizowa, Terry D. Macfarlane, and Paula J. Rudall. 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(1):179-200.Yadav SR, Janarthanam MK. 1995 Trithuria konkanensis (Hydatellaceae), eine neue Art aus Indien. Aqua Planta 20. (3): 91-97 (1995). Until DNA sequence data and a reinterpretation of morphology proved otherwise, these plants were believed to be monocots related to the grasses (Poaceae). They are unique in being the only plants besides two members of Triuridaceae (Lacandonia schizmatica and L. braziliana) in which the stamens are centred and surrounded by the pistils; in Hydatellaceae the resulting 'flowers' may instead represent condensed inflorescences or non-flowers.
These diminutive, superficially moss-like, aquatic plants are the closest living relatives of a clade comprising two closely related water-lily families Nymphaeaceae and Cabombaceae. Together, these three families compose the order Nymphaeales in the APG III system of flowering plant classification. Trithuria (Hydatellaceae) diverged from the rest of Nymphaeales soon after Nymphaeales diverged from its sister taxon, although the crown clade evolved relatively recently, in the early Miocene (~19 Ma;). The order as a whole is the sister group of all flowering plants except Amborellales.
Trithuria exhibits a remarkable similarity to Centrolepis and species of both genera were mistaken for members of the other genus.Sokoloff, D. D., Remizowa, M. V., Linder, H. P., & Rudall, P. J. (2009). "Morphology and development of the gynoecium in Centrolepidaceae: the most remarkable range of variation in Poales." American Journal of Botany, 96(11), 1925-1940.
Description
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. 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. Hydatellaceae are unusual among angiosperms in allocating nutrients to the embryo before fertilization. In all other flowering plants, nutrient provisioning is known to occur only after fertilization. This trait is similar to gymnosperms, although in gymnosperms the nutrients come from the gametophyte rather than maternal tissue.Hydatellaceae are water lilies with gymnospermous tendencies
Cytology The diploid chromosome count of Trithuria inconspicua subsp. inconspicua is 2n = c. 24. The diploid chromosome count of Trithuria submersa is 2n = 56.Flora of New Zealand | Taxon Profile | Trithuria. (n.d.). Retrieved July 26, 2023, from https://www.nzflora.info/factsheet/taxon/Trithuria.html The diploid chromosome count of the tetraploid species Trithuria konkanensis 2n = 40.Remizowa, M. V., Sokoloff, D. D., Macfarlane, T. D., Yadav, S. R., Prychid, C. J., & Rudall, P. J. (2008). "Comparative pollen morphology in the early‐divergent angiosperm family Hydatellaceae reveals variation at the infraspecific level." Grana, 47(2), 81-100. The diploid chromosome count of Trithuria australis is 2n = 14.Sokoloff, D. D., Marques, I., Macfarlane, T. D., Remizowa, M. V., Lam, V. K. Y., Pellicer, J., … Graham, S. W. (2019). Cryptic species in an ancient flowering-plant lineage (Hydatellaceae, Nymphaeales) revealed by molecular and micromorphological data. TAXON, 68(1), 1–19. doi:10.1002/tax.12026
Taxonomy The genus Trithuria was described by Joseph Dalton Hooker in 1858 with the type species Trithuria submersa It has two synonyms: In 1888 the genus Juncella was described without a type designationJuncella F.Muell. ex Hieron. (n.d.). The Australian National Species List (auNSL). Retrieved November 17, 2024, from https://biodiversity.org.au/nsl/services/rest/instance/apni/520743 by Georg Hans Emmo Wolfgang Hieronymus based on previous work by Ferdinand von Mueller. Mueller had invalidly published the nomen invalidum and nomen nudum Juncella tasmanica in 1854.Juncella tasmanica | International Plant Names Index. (n.d.). Retrieved November 18, 2024, from https://www.ipni.org/n/129787-3Juncella tasmanica F.Muell. (n.d.). The Australian National Species List (auNSL). Retrieved November 18, 2024, from https://biodiversity.org.au/nsl/services/rest/name/apni/96340/api/apni-format Juncella is a nomen illegitimum. In 1904 the genus Hydatella was described by Friedrich Ludwig Emil DielsHamann, U. (1976). Hydatellaceae—a new family of Monocotyledoneae. New Zealand Journal of Botany, 14(2), 193-196. without a type designation,Hydatella Diels. (n.d.). The Australian National Species List (auNSL). Retrieved November 17, 2024, from https://biodiversity.org.au/nsl/services/rest/name/apni/86441/api/apni-format but the lectotype Hydatella australis has been designated in 2008. The genus Hydatella was synonymised with Trithuria in 2008.
Trithuria was initially placed in the family Centrolepidaceae (now synonymous with Restionaceae ), which is placed in the order Poales Linder, H. P., & Rudall, P. J. (2005). Evolutionary history of Poales. Annu. Rev. Ecol. Evol. Syst., 36(1), 107-124. but it was separated as its own family Hydatellaceae by Ulrich Hamann in 1976Hamann, Ulrich | International Plant Names Index. (n.d.). Retrieved November 17, 2024, from https://www.ipni.org/a/5-1 with Hydatella as the type genus. Upon its separation, Hamann stated the new families affinity or placement were still obscure. The correct placement of the family became apparent in 2007, when it was identified as a basal angiosperm lineage. The family Hydatellaceae is now placed in the order Nymphaeales .WFO (2024): Nymphaeales Salisb. ex Bercht. & J. Presl. Published on the Internet;http://www.worldfloraonline.org/taxon/wfo-9000000354. Accessed on: 17 Nov 2024 Alternatively, it is placed in a separate order Hydatellales validly published by James Lauritz Reveal and Alexander Borissowitsch Doweld in 1999 based on previous work by Arthur Cronquist (see the Cronquist system).Doweld A.B. 2022. New names of fossil Nymphaeaceae and allied forms. Geophytology 52(1&2): 1–28.Reveal, J. L., & Doweld, A. B. (1999). Validation of Some Suprageneric Names in Magnoliophyta. Novon, 9(4), 549–553. https://doi.org/10.2307/3392163 This is however not widely accepted, as the order Hydatellales is mostly treated as a synonym of Nymphaeales.Manaaki Whenua – Landcare Research. (n.d.-b). Nymphaeales Salisb. ex Bercht. & J.Presl. Flora of New Zealand Online. Retrieved November 17, 2024, from https://www.nzflora.info/factsheet/taxon/Nymphaeales.htmlReveal, J. L. (2012). An outline of a classification scheme for extant flowering plants. Phytoneuron, 37(1), 1-221.Reveal, J. L., & Chase, M. W. (2011). APG III: Bibliographical information and synonymy of Magnoliidae. Phytotaxa, 19, 71-134. Etymology The generic name Trithuria is derived from the Greek words τρεις treis meaning "three", and θυρις thyris meaning "window". It references the dehiscence of the capsule fruit.Hooker, Joseph Dalton, Fitch, W. H., & Reeve Brothers. (1844). The botany of the Antarctic voyage of H.M. discovery ships Erebus and Terror in the Years 1839-1843 :under the command of Captain Sir James Clark Ross (Vol. 3, Issue 2, pp. 78-79). Reeve Brothers. https://www.biodiversitylibrary.org/page/28467263Department for Environment and Water. (n.d.). Trithuria submersa (Hydatellaceae) | Seeds of South Australia - Species information. Retrieved July 26, 2023, from https://spapps.environment.sa.gov.au/SeedsOfSA/speciesinformation.html?rid=4619 Species Trithuria has 13 species, although species diversity in the family has probably been substantially underestimated.
Trithuria austinensis D.D.Sokoloff, Remizowa, T.D.Macfarl. & Rudall Western Australia Trithuria australis (Diels) D.D.Sokoloff, Remizowa, T.D.Macfarl. & Rudall - Western Australia Trithuria bibracteata Stapf ex D.A.Cooke - Western Australia Trithuria cookeana D.D.Sokoloff, Remizowa, T.D.Macfarl. & Rudall - Northern Territory of Australia Trithuria cowieana D.D.Sokoloff, Remizowa, T.D.Macfarl. & Rudall - Northern Territory Trithuria filamentosa Rodway - Tasmania Trithuria fitzgeraldii D.D.Sokoloff, I.Marques, T.D.Macfarl., Rudall & S.W.Graham - Western Australia Trithuria inconspicua Cheeseman - North Island of New ZealandTrithuria inconspicua subsp. brevistyla K.A.Ford - endemic to South Island, New Zealand Trithuria konkanensis S.R.Yadav & Janarth. - Maharashtra Trithuria lanterna D.A.Cooke - Northern Territory, Western Australia, Queensland Trithuria occidentalis Benth. - Western Australia Trithuria polybracteata D.A.Cooke ex D.D.Sokoloff, Remizowa, T.D.Macfarl. & Rudall - Western Australia Trithuria submersa Hook.f. - Western Australia, South Australia, Victoria, New South Wales, Tasmania
Distribution and habitat It is native to India, Australia, and New Zealand, where it occurs in seasonally dry aquatic environments as annuals, or more rarely in permanently inundated habitats as perennial plants.Taylor, M. L., Macfarlane, T. D., & Williams, J. H. (2010). Reproductive ecology of the basal angiosperm Trithuria submersa (Hydatellaceae). Annals of Botany, 106(6), 909-920.
Conservation The IUCN conservation status of Trithuria lanterna is Least Concern (LC).Brummitt, N. 2013. Trithuria lanterna. The IUCN Red List of Threatened Species 2013: e.T44392948A44408157. https://dx.doi.org/10.2305/IUCN.UK.2013-1.RLTS.T44392948A44408157.en. Accessed on 13 December 2024. Trithuria inconspicua is critically endangered.Critically endangered Northland lake plant voted NZ's favourite plant 2024. (2024, November 5). Northland Regional Council. Retrieved December 13, 2024, from https://www.nrc.govt.nz/news/2024/november/critically-endangered-northland-lake-plant-voted-nz-s-favourite-plant-2024/
References
External links Hydatellaceae in L. Watson and M.J. Dallwitz (1992 onwards).,The families of flowering plants: descriptions, illustrations, identification, information retrieval. Version: 27 April 2006. https://web.archive.org/web/20060424062016/http://delta-intkey.com/ Hydatellaceae photographs NCBI Taxonomy Browser