Brasenia schreberi aka Schreber's Watershield

Brasenia schreberi is challenging to cultivate because it requires very specific aquatic conditions that most gardeners cannot easily provide. The plant needs still or slow-moving, lime-free water with mildly acidic to neutral pH, full sun exposure (it cannot tolerate shade), and muddy substrate at water depths between 8 inches and 6 feet. Once these conditions are established, the plant requires low maintenance, but creating and maintaining the proper aquatic habitat is the primary difficulty.

Brasenia schreberi is a thermophilic (warmth-loving) aquatic species that thrives in USDA hardiness zones 6-9. It naturally occurs in subtropical regions below 40°N latitude and tolerates a range of temperatures during the growing season. In colder climates, the plant dies back in winter with rhizomes surviving in the muddy substrate. PFAF notes that in greenhouse cultivation, a minimum temperature of 18°C (64°F) should be maintained during winter.

Brasenia schreberi generally does not require supplemental fertilization when grown in natural pond conditions. The plant obtains nutrients from the muddy substrate through its rhizomatous root system. In fact, it naturally prefers oligotrophic to mesotrophic (low to moderate nutrient) water conditions. Excessive nutrients can promote algae growth that may compete with or shade the plant, so avoid fertilizing directly and maintain clean, clear water.

Brasenia schreberi can be propagated by seed or division. For seed propagation, sow seeds as soon as they are ripe since aquatic plant seeds lose viability quickly if allowed to dry out. Store seeds in water until sowing in spring if immediate sowing isn't possible. Grow seedlings in pots barely covered with water, increasing depth as plants grow, and transplant to permanent positions in late spring after the last frost. Division of the creeping rhizomes is the easier method and can be done in spring or early summer.

Brasenia schreberi produces small but attractive flowers from June through August. Each flower measures about ¾ inch across and rises on a stout stalk up to 4 inches above the water surface. The flowers display 3-4 petals in colors ranging from dull purplish-brown to pinkish-red, with similar-looking sepals and numerous erect stamens. The plant exhibits a fascinating two-day blooming cycle: on day one the flower emerges as female with receptive stigmas, retreats underwater, then emerges on day two as male to release pollen before submerging for fruit development.

Brasenia schreberi is pollinated primarily by beetles, with wind serving as a secondary pollinator. The plant is hermaphroditic, containing both male and female reproductive organs, but uses a clever mechanism to promote cross-pollination. Each flower opens for exactly two days: emerging first as a female flower with receptive stigmas, then retreating underwater and re-emerging the next day as a male flower to release pollen. This sequential hermaphroditism ensures that self-pollination is minimized and genetic diversity is maintained.

Brasenia schreberi is exclusively an outdoor aquatic plant that grows in ponds, lakes, and slow-moving streams. It thrives in USDA hardiness zones 6-9 and requires full sun exposure. The plant needs still or slow-moving lime-free water at depths from 8 inches to 6 feet, with roots anchored in muddy substrate. In colder zones, rhizomes can overwinter in the mud if the pond doesn't freeze solid to the bottom.

During spring and summer, Brasenia schreberi actively grows and flowers, requiring full sun and stable water levels. This is the best time to harvest young leaves for culinary use (particularly in spring when the mucilage coating is thickest) and to propagate by division. In autumn, the plant produces seeds and begins to die back as temperatures drop. During winter, the rhizomes remain dormant in the mud—no active care is needed if the pond doesn't freeze solid to the bottom. Resume watching for new growth in spring when water temperatures warm.

Brasenia schreberi has few pest and disease problems, likely due to its distinctive gelatinous mucilage coating that covers all underwater parts. This slime-like substance appears to deter herbivory by mammals and may have antibacterial properties. The main threats are environmental rather than biological: water pollution, habitat degradation, and excessive algae growth from nutrient runoff can harm the plant. Maintaining clean, oligotrophic to mesotrophic water conditions is the best preventive care.

Brasenia schreberi is edible and has been cultivated as an aquatic vegetable in East Asia for over 3,000 years. Known as 'Junsai' in Japan, the young leaf tips coated with their characteristic mucilage are considered a delicacy. They are harvested in spring and eaten raw as salad with vinegar, sake, and soy sauce, or added to soups as a thickener. The roots can be peeled, boiled, and eaten, or dried and ground into flour for later use. Young stems can also be eaten raw or cooked. PFAF rates edibility as 3 out of 5.

Brasenia schreberi has traditional medicinal applications, particularly in East Asian medicine. The astringent leaves are crushed and applied topically to treat abscesses and boils. The plant has been used traditionally for dysentery and various ailments. Modern research has confirmed that the mucilage exhibits antibacterial, anti-inflammatory, and antioxidant properties. The slimy coating may help soothe irritated or dry skin. A decoction of the seeds has been used as an antidote in traditional medicine. PFAF rates medicinal value as 2 out of 5.

Beyond food and medicine, Brasenia schreberi has allelopathic (phytotoxic) properties, meaning it naturally produces chemicals that suppress the growth of nearby plants. This characteristic makes it potentially useful for natural control of invasive aquatic weeds without herbicides. The plant also provides ecological benefits: its floating leaves offer shelter for fish and aquatic organisms, and its fruits are consumed by waterfowl. PFAF rates other uses as 2 out of 5.

Brasenia schreberi grows as a spreading aquatic perennial with creeping rhizomes anchored in muddy substrate. The plant reaches only about 4 inches (0.1 m) in vertical height above the water surface, but spreads horizontally up to 6 feet (2 m). It produces long, slender, branching stems with floating, oval leaves measuring 2.5-5 inches long. Growth rate is moderate, less vigorous than water lilies. The distinctive gelatinous mucilage coating all underwater parts is a unique identifying feature.

Schreber's Watershield’s native range is N. America - Nova Scotia to Manitoba and Nebraska, south to Florida, Texas and Mexico.

Schreber's Watershield should be watered regularly, allowing the soil to dry out between waterings.

Schreber's Watershield is very sensitive to dry soil. To ensure your Water Shield is thriving and blooming, choose a potting soil that retains moisture. A good soil should still allow for adequate drainage and contain lots of organic matter. Coco coir or sphagnum moss are great soil additives that will help to retain moisture and provide your Schreber's Water Shield with the nutrients it needs for healthy growth. Make sure to mix these soil additives into the potting soil before planting and water the soil thoroughly. By providing your Schreber's Watershield with a well-draining, moisture-retaining soil, you can help to maximize its growth and keep it blooming.

Schreber's Watershield requires abundant, bright, and direct light to thrive. The best placement for this plant is within one foot of a window to ensure it receives enough light. If you live in an area with more extreme weather, such as hot summers or cold winters, you may need to adjust the placement of the plant accordingly. During hot summer months, it is important to place the plant away from full sun, as this can cause the leaves to yellow or burn. During cold winter months, it is best to move the plant closer to the window to take advantage of the extra light that can help it survive. By keeping an eye on the current weather in your area, you can make sure your Water Shield is always in the right place to thrive.

Ploi lacks confirmed information on the toxicity of this plant. If you, a relative, or your pet accidentally consume plant material with unknown toxicity, it's best to consult a medical expert.