Trithuria

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.[1][2] All of the 13 formally characterized species of Trithuria are found in Australia, with the exception of T. inconspicua and T. konkanensis, which are found in New Zealand and India, respectively.[3][4] 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 in the center of the flower while the pistils surround them; in Hydatellaceae the resulting 'flowers' may instead represent condensed inflorescences or non-flowers.[5]

Trithuria
Trithuria submersa
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Order: Nymphaeales
Family: Hydatellaceae
Genus: Trithuria
Hook.f.
Type species
Trithuria submersa
Synonyms[1]
  • Hydatella Diels
  • Juncella F.Muell. ex Hieron.

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.[6] 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;[7]). 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.[8]

Taxonomy

The genus Hydatella was subsumed into Trithuria as its members are phylogenetically nested in it. The family as a whole shares the following features (morphological synapomorphies[3])

  • lack of a vascular cambium
  • lack of pericyclic sclerenchyma
  • anomocytic stomata
  • truncate anther connective
  • boat-shaped pollen
  • inner integument with two cell layers
  • palisade exotesta
  • seed operculum formed by cell enlargement in the inner integument
  • perisperm
  • hypogeal germination.[9]

Species and distribution
Phylogeny of Trithuria[10][11]
sect. Altofinia

T. cookeana

T. cowieana

sect. Hamannia

T. polybracteata

T. konkanensis

T. lanterna

sect. Trithuria

T. occidentalis

T. bibracteata

T. submersa

sect. Hydatella

T. austinensis

T. australis

T. filamentosa

T. inconspicua

  1. Trithuria austinensis D.D.Sokoloff - Western Australia
  2. Trithuria australis (Diels) D.D.Sokoloff - Western Australia
  3. Trithuria bibracteata Stapf ex D.A.Cooke - Western Australia
  4. Trithuria cookeana D.D.Sokoloff, Remizowa, T.D.Macfarl. & Rudall - Northern Territory of Australia
  5. Trithuria cowieana D.D.Sokoloff - Northern Territory
  6. Trithuria filamentosa Rodway - Tasmania
  7. Trithuria fitzgeraldii D.D.Sokoloff, I.Marques, T.D.Macfarl., Rudall & S.W.Graham - Western Australia
  8. Trithuria inconspicua Cheeseman - North Island of New Zealand
  9. Trithuria konkanensis S.R.Yadav & Janarth. - Maharashtra
  10. Trithuria lanterna D.A.Cooke - Northern Territory, Western Australia, Queensland
  11. Trithuria occidentalis Benth. - Western Australia
  12. Trithuria polybracteata D.A.Cooke ex D.D.Sokoloff, Remizowa, T.D.Macfarl. & Rudall - Western Australia
  13. Trithuria submersa Hook.f. - Western Australia, South Australia, Victoria, New South Wales, Tasmania

Etymology

The generic name Trithuria is composed of two parts: the Greek words treis meaning "three", and thyris meaning "window". It references the dehiscence of the fruit.[12] Specifically, it references the pericarp valves of some Trithuria species.[13]

Cytology

The diploid chromosome count of Trithuria inconspicua subsp. inconspicua is 2n = c. 24. The diploid chromosome count of Trithuria submersa is 2n = 56.[13] The diploid chromosome count of the tetraploid species Trithuria konkanensis 2n = 40.[14] The diploid chromosome count of Trithuria australis is 2n = 14.[15]

References
  1. Kew World Checklist of Selected Plant Families
  2. Marques, Isabel; Montgomery, Sean A.; Barker, Michael S.; Macfarlane, Terry D.; Conran, John G.; Catalán, Pilar; Rieseberg, Loren H.; Rudall, Paula J.; Graham, Sean W. (2016-04-01). "Transcriptome-derived evidence supports recent polyploidization and a major phylogeographic division in Trithuria submersa (Hydatellaceae, Nymphaeales)". New Phytologist. 210 (1): 310–323. doi:10.1111/nph.13755. ISSN 1469-8137. PMID 26612464.
  3. 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.
  4. Yadav SR, Janarthanam MK. 1995 Trithuria konkanensis (Hydatellaceae), eine neue Art aus Indien. Aqua Planta 20. (3): 91-97 (1995).
  5. Rudall, Paula J. (February 4, 2016). "Inside-out flowers of Lacandonia brasiliana (Triuridaceae) provide new insights into fundamental aspects of floral patterning". PeerJ. 4: e1653. doi:10.7717/peerj.1653. PMC 4748704. PMID 26870611.
  6. Else Marie Friis & Peter Crane (15 March 2007), "Botany: New home for tiny aquatics", Nature, 446 (7133): 269–270, Bibcode:2007Natur.446..269F, doi:10.1038/446269a, PMID 17361167
  7. Iles, William J D; Lee, Christopher; Sokoloff, Dmitry D; Remizowa, Margarita V; Yadav, Shrirang R; Barrett, Matthew D; Barrett, Russell L; Macfarlane, Terry D; Rudall, Paula J; Graham, Sean W (2014). "Reconstructing the age and historical biogeography of the ancient flowering-plant family Hydatellaceae (Nymphaeales)". BMC Evolutionary Biology. Springer Science and Business Media LLC. 14 (1): 102. doi:10.1186/1471-2148-14-102. ISSN 1471-2148. PMC 4030046.
  8. 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.
  9. Jeffery M. Saarela1; et al. (15 March 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, S2CID 4415881
  10. Sokoloff, Dmitry D.; Remizowa, Margarita V.; Beer, Anton S.; Yadav, Shrirang R.; Macfarlane, Terry D.; Ramsay, Margaret M.; Rudall, Paula J. (May 2013). "Impact of spatial constraints during seed germination on the evolution of angiosperm cotyledons: A case study from tropical Hydatellaceae (Nymphaeales)". American Journal of Botany. 100 (5): 824–843. doi:10.3732/ajb.1200620. PMID 23613353.
  11. Iles, Will; Rudall, Paula J.; Sokoloff, D. D.; Graham, Sean W (March 2012). "Molecular phylogenetics of Hydatellaceae (Nymphaeales): Sexual-system homoplasy and a new sectional classification". American Journal of Botany. 99 (4): 663–676. doi:10.3732/ajb.1100524. PMID 22473977.
  12. Department 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
  13. Flora of New Zealand | Taxon Profile | Trithuria. (n.d.). Retrieved July 26, 2023, from https://www.nzflora.info/factsheet/taxon/Trithuria.html
  14. 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.
  15. 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
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