Trithuria

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

The genus Trithuria was described by Joseph Dalton Hooker in 1858 with the type species Trithuria submersa by Georg Hans Emmo Wolfgang Hieronymus based on previous work by Ferdinand von Mueller. Juncella is a nomen illegitimum. without a type designation, but the lectotype Hydatella australis has been designated in 2008. (now synonymous with Restionaceae ), which is placed in the order Poales but it was separated as its own family Hydatellaceae by Ulrich Hamann in 1976 with Hydatella as the type genus. Upon its separation, Hamann stated the new families affinity or placement were still obscure. 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). This is however not widely accepted, as the order Hydatellales is mostly treated as a synonym of Nymphaeales. Hydatellales Hydatellales is a botanical name for an order of flowering plants. In the Cronquist system, 1981, the name was used for an order placed in the subclass Commelinidae in class Liliopsida [=monocotyledons]. The order consisted of one family only: Hydatellaceae Similarly the Dahlgren system recognised this order (with the same circumscription and placed it in superorder Commelinanae in subclass Liliidae [=monocotyledons]. The APG II system assigned these plants to the order Poales, close to the grasses and sedges. Recent study by Saarela et al., however, suggests a position out of the Poales; here, the Hydatellaceae link with the waterlilies, the first time a plant has been ejected from the monocots. The Angiosperm Phylogeny Website had since updated the Nymphaeales page to include the family. Hydatellaceae Hydatellaceae are a family of small, aquatic flowering plants that includes only the genus Trithuria Hook.f., which in 2008 was re-defined to include the genus Hydatella Diels. The type species is Trithuria submersa Hook.f. 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. Species and distribution Trithuria has at least 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 ==Conservation==

The IUCN conservation status of Trithuria lanterna is Least Concern (LC). Trithuria inconspicua is critically endangered. ==References==