Brasenia

Lore & Background

Brasenia schreberi, known as watershield, is a perennial aquatic plant that grows in shallow water of lakes, rivers, and beaver ponds, particularly those with somewhat acidic water. It is identified by its bright green leaves, small purple flowers that bloom from June through September, and a thick mucilage covering the underside of leaves, stems, and developing buds. This mucilage may be an anti-herbivore defense, possibly to deter snail grazing.

The flowers exhibit wind pollination with a two-day blooming period. On the first day, the functionally female flower extends above the water, exposing receptive stigmas, then recedes. On the following day, it emerges as a functionally male flower, elevated higher, with anthers releasing pollen before the flower withdraws underwater for fruit development.

Historically, species of Brasenia occurred during the interglacial of Europe but do not occur there now. The genus may commemorate surgeon and Moravian missionary Christoph Brasen (1738–1774), first superintendent of the Moravian mission at Nain in Labrador.

Reader's Guide

Brasenia schreberi holds significance both ecologically and culturally. Ecologically, its thick mucilage may serve as an anti-herbivore defense, potentially deterring snail grazing, and has been found to have anti-algal and anti-bacterial properties that could be useful as a natural weed control. The plant is cultivated as a vegetable in China, where it is known as chúncài (莼菜) and used in the well-known local specialty 'West Lake Water Shield Soup' in Hangzhou, as well as in Japan. Its conservation status varies: globally it is classified as Least Concern by the IUCN, but it is considered Vulnerable in South Korea and Critically Endangered under the Flora and Fauna Guarantee Act 1988 in Victoria, Australia. The NatureServe conservation status is G5 Secure. The plant's unique reproductive strategy—wind pollination with a two-day, sex-changing flower—and its large mitochondrial genome (1.49 Mb) add to its biological interest. Its historical presence in European interglacial periods, though now absent there, underscores its relictual distribution.

Did You Know?

• Brasenia schreberi is the only species in the genus Brasenia.
• The thick mucilage covering its underwater organs may deter snail grazing.
• Its flowers are wind-pollinated and change from female to male over two days.
• It is cultivated as a vegetable in China and Japan, notably in 'West Lake Water Shield Soup'.