This unusual, rare plant has oval leaves that float on the water surface when grown in shallow water, but narrow long leaves in deeper areas where it can be grown up to 4m deep. It flowers prolifically when very shallow or on bare mud, with little white flowers and a yellow centre.

Luronium natans, commonly known as floating water-plantain, is a submerged aquatic plant native to Europe and parts of Asia. It typically grows in slow-moving or stagnant water bodies such as ponds, lakes, and marshes. Here is a general care guide for submerged aquatic plants that may be helpful:

Water and Light Requirements: Submerged aquatic plants like Luronium natans require clear, still water with ample sunlight. They thrive in full sun to partial shade. Make sure that the water has sufficient nutrients and is not heavily polluted.

Water Depth: Floating water-plantain is a fully submerged plant that grows in water depths of up to several feet. Ensure that the water is deep enough to accommodate the plant's growth without restricting its development.

Water Temperature: Luronium natans prefers cool to moderate water temperatures. It can tolerate a range of temperatures but generally does best in the 60-75°F (15-24°C) range. Extreme temperatures, both hot and cold, can stress or damage the plant.

Water Quality: The water quality should be good, with low levels of pollutants and high oxygen content. Regular water testing and maintenance, including water circulation and aeration, can help maintain suitable water conditions for the plant's health.

Planting: Submerged aquatic plants are typically planted in containers or baskets filled with aquatic soil or gravel. This helps to anchor the plant and provide nutrients. Ensure that the containers have drainage holes to prevent waterlogging. Gently place the plant in the container, covering the roots with the substrate, and then submerge the container in the desired location in the water.

Maintenance: Regular maintenance is essential for the health of submerged aquatic plants. This includes removing any dead or decaying plant material, controlling excessive algae growth, and periodically trimming the plant to maintain its desired size and shape. Be careful not to disturb the root system while performing these tasks.

Propagation: Luronium natans can propagate through seed production, but it can also spread by rhizome growth and division. If the plant becomes overcrowded, you can divide the rhizomes and replant them in suitable locations.

It's important to note that specific care requirements may vary based on the particular needs of Luronium natans as well as your local climate and growing conditions. If possible, consult with local horticulturists, aquatic plant specialists, or experienced gardeners who have knowledge about this particular plant to get more accurate care instructions and recommendations.