Subordinate Taxa
Scientific Name:
Trithuria Hook.f., Bot. Antarct. Voy. III. (Fl. Tasman.) Part II, 78, pl. 137, fig. 1 (1858)
  • = Juncella F.Muell. ex Hieron. in Engler & Prantl, Nat. Pflanzenfam.II, 4, 15 (1888)
Type not designated
  • = Hydatella Diels in Diels & Pritzel, Bot. Jahrb. Syst. 35: 93, fig.7 (1904)
Lectotype: Hydatella australis Diels (≡ Trithuria australis (Diels) D.D.Sokoloff, Remizowa, T.D.Macfarl. & Rudall, Taxon 57(1): 193 (2008))
Type Taxon:
Trithuria submersa Hook.f.
Three windowed (Greek), named for the pericarp valves in some species (not NZ).

Perennial (NZ & Tasmania) or annual herbs; tufted from an erect, shortly branching rhizome. Coteylodons free or united. Leaves spiral, 1-veined; lamina linear-filiform, air canals well developed. Reproductive unit an involucre of hyaline bracts 2–30 (NZ mostly 2 or 4). Stamens 1–17 per reproductive unit; anthers 0.3–2.8 mm long basifixed on filaments 1–5 mm long; pollen oblong or rounded, monosulcate, tectum perforate, exine surface microechinate. Carpels (2–)10–40 per reproductive unit, stipitate, on persistent stalks; uniseriate stigmatic hairs 0.2–5.0 mm long. Fruits dehiscent (2 or 3-valved) or indehiscent. Seeds sculptured or not.


Most species are semi-aquatic annuals (of Australia) associated with seasonal ephemeral pools and wetlands, two species are fully aquatic perennials of permanent lakes, one in New Zealand and the other in Tasmania. Recent molecular phylogenetic analyses of Trithuria have resolved four lineages that Iles et al. (2012) have formerly classified into taxonomic sections, diagnosable by fruit and seed characters. Trithuria inconspicua is a sister species to T. filamentosa of Tasmania and both are classified in section Hydatella (Iles et al. 2012, 2014) along with T. austinensis and T. australis of Western Australia. This section is diagnosed on the basis of: an absence of pericarp ribs and papillae, a thick seed cuticle, and possibly the presence of leaf-sheath auricles (Iles et al. 2012).

Trithuria is adapted to wind pollination (Taylor et al. 2010) and not submerged hydrophily, despite flowers opening underwater (Edgar 1966). In T. submersa Taylor et al. (2010) showed that emergence was necessary for both pollen release and reception. Species of Trithuria have evolved both strong selfing and outcrossing breeding systems (Taylor & Williams 2012) and exhibit dioecy, autogamy and apomixis. Evidence for apomixis in T. inconspicua and T. filamentosa is based on near permanent submergence of flowering plants below the water surface (Edgar 1966) and rarely emergent except during prolonged drought conditions; by pollen abnormalities (Hamann 1976, Remizowa et al. 2008); and by embryo development with an absence of pollen tubes (Rudall et al. 2008). Genetic population studies (Smissen et al. 2019) have provided further evidence that T. inconspicua and its sister species T. filamentosa are apomictic, although possibly with a recent history of at least occasional sexual reproduction.


The minute tufts with monocot-like linear leaves are very different to the macrophytes of Cabombaceae and Nymphaeaceae. Trithuria also differs significantly in flower morphology, with non-showy bracted ‘reproductive units’ (flowers or inflorescences) and with stalked, free carpels with multiseptate stigmatic hairs directly attached to the carpel apex. Most species are semi-aquatic (ex T. filamentosa and T. inconspicua) and inhabit ephemeral water-bodies that are flowering and fruiting above the receding waterline.


Trithuria Hook.f. has 13 species; 11 endemic to Australia, and 1 endemic to each of New Zealand and India (Sokoloff et al. 2008).

Indigenous (Non-endemic)
Number of species in New Zealand within Trithuria Hook.f.
Indigenous (Endemic)1
Cronquist, A. 1988: The evolution and classification of flowering plants. The New York Botanic Gardens, New York.
de Lange, P.J.; Murray, B.G.; Datson, P.M. 2004: Contributions to a chromosome atlas of the New Zealand flora – 38. Counts for 50 families. New Zealand Journal of Botany 42: 873–904.
Diels, F.L.E.; Pritzel, E. 1904: Fragmenta Phytographiae Australiae occidentalis. Beiträge zur Kenntnis der Pflanzen Westaustraliens, ihrer Verbreitung und ihrer Lebensverhältnisse. Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie 35(2): 55–662.
Edgar, E. 1966: The male flowers of Hydatella inconspicua (Cheesem.) Cheesem. (Centrolepidaceae). New Zealand Journal of Botany 4: 153–158.
Engler, H.G.A.; Prantl, K.A.E. 1888: Natürlichen Pflanzenfamilien II Teil, IV Abteilung. Leipzig.
Ford, K.A.; Champion, P.D. 2019: Nymphaeales. In: Breitwieser, I.; Wilton, A.D. (ed.) Flora of New Zealand - Seed Plants. Fascicle 5. Manaaki Whenua Press, Lincoln.
Hamann, U. 1976: Hydatellaceae – A new family of Monocotyledoneae. New Zealand Journal of Botany 14(2): 193–196.
Hooker, J.D. 1858–1859: 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. III. Flora Tasmaniae. Part II. Monocotyledones and acotyledones. Lovell Reeve, London.
Iles, W.J.D.; Lee, C.; Sokoloff, D.D.; Remizowa, M.V.; Yadav, S.R.; Barrett M.D.; Barrett, R.L.; MacFarlane, T.D.; Logacheva, M.D.; Rudall, P.J.; Graham, S.W. 2014: Reconstructing the age of the ancient flowering-plant family Hydatellaceae (Nymphaeales). BioMed Central Evolutionary Biology 14: 102.
Iles, W.J.D.; Rudall, P.J.; Sokoloff, D.D.; Remizowa, M.V.; MacFarlane, T.D.; Logacheva, M.D.; Graham, S.W. 2012: Molecular phylogenetics of Hydatellaceae (Nymphaeales): sexual-system homoplasy and a new sectional classification. American Journal of Botany 99: 663–676.
Kynast, R.G.; Joseph, J.A.; Pellicer, J.; Ramsay, M.M.; Rudall, P.J. 2014: Chromosome behaviour at the base of the angiosperm radiation: Karyology of Trithuria submersa (Hydatellaceae, Nymphaeales). American Journal of Botany 101: 1447–1455.
Mabberley, D.J. 2008: Mabberley's plant book, a portable dictionary of plants, their classification and uses. Edition 3. Cambridge University Press.
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: 81–100.
Rudall, P.J.; Remizowa, M.V.; Beer, A.S.; Bradshaw, E.; Stevenson, D.W.; Macfarlane, T.D.; Tuckett, R.E.; Yadav, S.R.; Sokoloff, D.D. 2008: Comparative ovule and megagametophyte development in Hydatellaceae and water lilies reveal a mosaic of features among the earliest angiosperms. American Journal of Botany 101: 941–956.
Smissen, R.D.; Ford, K.A.; Champion, P.D.; Heenan, P.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 32: 1–11.
Sokoloff, D.D.; Remizowa, M.V.; Macfarlane, T.D.; Rudall, P.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(1): 179–200.
Taylor, M.L.; Macfarlane, T.D.; Williams, J.H. 2010: Reproductive ecology of the basal angiosperm Trithuria submersa (Hydatellaceae). Annals of Botany 106: 909–920.
Taylor, M.L.; Williams, J.H. 2012: Pollen tube development in two species of Trithuria (Hydatellaceae) with contrasting breeding systems. Sexual Plant Reproduction 25: 83–96.