J. F. Gmel.
Brasenia is a genus belonging to the family Cabombaceae, consisting of one extant species widely distributed in warm temperate and tropical regions of the world. Brasenia is an perennial aquatic plant with floating, peltate leaves and rhizomatous stems. It is identified by its bright green leaves, small purple flowers that bloom from June through September, and a thick mucilage that covers all of the underwater organs, including the underside of the leaves, stems, and developing buds. This mucilage may be an anti-herbivore defence trait, perhaps to deter snail grazing. It grows in shallow water of lakes, rivers and beaver ponds, particularly those with somewhat acidic water.
Brasenia exhibits wind pollination. The flowers have a two-day blooming period. On the first day, the functionally female, or pistillate flower, extends above the surface of the water and exposes the receptive stigmas. The flower then recedes below the water surface and on the following day emerges as a functionally male, or staminate flower. It is elevated higher than on the previous day and the anther-bearing filaments are extended beyond the female carpels. The anthers dehisce, releasing the pollen, and the flower is then withdrawn below the water where the fruit develops.
Economically, Brasenia is cultivated as a vegetable in China and Japan (where it is known as junsai) and the mucilage it produces has been found to have anti-algal and anti-bacterial properties that may be useful as a natural weed control.
Brasenia occurred during the interglacial of Europe, but like some other aquatic species, it does not occur there now.
Brasenia schreberi (syn. B. nymphoides, B. peltata) has the common name water-shield (also watershield or water shield).
- Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. Figure 6.9
- Taylor,Mackenzie L. and Jeffrey M. Osborn. 2006. Pollen ontogeny in Brasenia (Cabombaceae, Nymphaeales). American Journal of Botany 93: 344-356
- Sculthorpe, C. D. 1967. The Biology of Aquatic Vascular Plants. Reprinted 1985 Edward Arnold, by London. p. 404.
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- Washington State Department of Ecology: Brasenia schreberi
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