Luronium natans is an aquatic plant that is more commonly known as floating water plantain or floating frog weed. Endemic to Europe, it belongs to the Alismataceae family, which includes around 90 species of flowering herbs that grow in ponds and marshes. These species are often collectively referred to as water-plantains and exhibit multiple forms depending on their location relative to water.

Luronium natans is one of the trickiest to identify and is often confused with Baldellia ranunculoides (lesser water-plantain) and Alisma plantago-aquatica (water-plantain). It is distinguished from these species by its pseudostolons, which are actually modifications of stem inflorescences.

The main reason for the difficulty in identifying this species is the variability of its features. Floating water plantain has two distinct forms. When completely submerged in freshwater, this plant produces rosettes of flat linear leaves that extend to 60 cm (24 inches) long. These leaves appear to be translucent underwater and will wither when exposed to air.

Luronium natans second form is suited to more exposed or shallow water conditions. It is characterized by leathery expanded leaves that float on the water’s surface. These leaves have petioles attaching them to ascending stems. Occasionally, this plant produces solitary, three-petaled, white flowers. It does not solely rely on these for reproduction, however, as it can spread by vegetative means.

Facts, Benefits & Uses of Floating Water Plantain

This nitrate-removing species is suitable for cultivation as an ornamental aquatic plant. Unfortunately, natural populations of floating water plantain are in steady decline due to habitat loss, competition with invasive species, and water pollution across their native range. This species is now considered rare in Central and Northern Europe and is listed under Appendix I of the Bern Convention of strictly protected flora. This convention prohibits the collection of this species from the wild.

Several initiatives in the UK have sought to protect wild populations by providing sanctuary areas and by implementing reserves in cases where dredging or canal restoration projects could cause damage to the local ecology.

Regrettably, the status of this otherwise highly adaptable plant may be considered inaccurate due to both its plasticity and survey-related limitations. Its potential to spread in range is presumably high because it can tolerate a wide variety of habitats, such as ponds and pools with standing water, flowing water bodies like streams and rivers, and artificial water bodies as well. Yet, its sensitivity to pollution limits its survivability throughout these areas.

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Floating Water Plantain Growth, Hardiness & Climate

Floating water plantain is highly sensitive to polluted waters. This signifies its importance in the realm of freshwater conservation. It can thrive in both oligotrophic and mesotrophic bodies of water, up to a depth of 2 meters (6.5 feet). Its preference for clear cool water highlights its sensitivity to algal growth and turbidity. For this reason, this ornamental plant can be grown in shallow garden ponds, where its floating leaves can provide adequate surface cover.

This species is considered a lowland plant, and its known altitudinal limit is 450 meters (1,480 feet). It is quite winter hardy and tolerates a wide variety of substrates, though its likelihood of flowering is associated with clay soil. It thrives in moderately nutrient-rich soil conditions and prefers acidic pH levels. It is typically perennial when cultivated in water, but may arise as an annual along the margins of water bodies. This occurs when water levels fluctuate, as the plant is unable to withstand extended periods of desiccation.

How to Plant Floating Water Plantain

Floating water plantain can be quite challenging to grow from seed. If you intend to grow this species in your pond, it would be best to acquire either a bare-rooted plant or runners. Allow these to take root and establish themselves in aquatic soil, preferably in a pot or mesh basket that can easily be lowered into your pond. Do note that this plant’s flowering form flourishes under shallow water conditions, so make sure to select for the appropriate pot height. Moreover, a bare mud setup along the margin of your pond may further encourage flowering.

As an oxygenator, this species may also be a beneficial addition to the deeper sections of your pond. Keep in mind that it will develop linear leaves this way, and will likely maintain an almost fully submerged, vegetative habit. Place the plant no deeper than 20 cm in your pond until it is fully established. It can be moved further into the pond over time. Top gravel can be used to weigh down the soil and protect the crown of the plant from inquisitive pond inhabitants.

How to Care For Floating Water Plantain

Though this species can withstand partial shade, its leaves will appreciate full exposure. Maintain and regularly prune plants along your pond’s margins to prevent them from overshadowing your floating water plantain community. As it prefers acidic-neutral soil and water environments, regularly check your pond’s pH levels. Make sure to provide your pond with a proper filtration system to prevent nutrient build-ups, which can be detrimental to this plant.

Floating water plantain is not biologically equipped to withstand murky or heavy algal conditions. It would be best grown alongside other species that can effectively provide shade to prevent algal buildup. Regularly check for pests or decayed areas on the plant’s foliage, and trim any compromised or diseased leaves.

How to Winter Floating Water Plantain

Floating water plantain is a frost-hardy perennial that can withstand outdoor winter conditions. As winter approaches, carefully trim any foliage that has dried out or died back. If located in an area where winter conditions may cause your pond’s surface to freeze over, you may want to move your pots deeper into your pond (to protect the crowns of the plants). Re-locate them to shallower/marginal areas once more as spring approaches so that the plant can produce expanded leaves. If you have juvenile plants or runners that are not fully established by autumn, consider transferring your plant to a greenhouse. If doing so, make sure to keep the plant submerged throughout winter as it will not survive desiccation.

This rare plant is not at all considered invasive, and is perhaps the antithesis of invasive plants! It has not been shown to proliferate in the wild outside of its native range and may even be challenging to grow in ponds outside of USDA 6. It is unfortunately not the most formidable of plant competitors, as it is sensitive to ecological change and water quality. One of the biggest threats to its survival is other invasive species that may choke its growth by claiming space, blocking out light, and taking away necessary nutrients for growth. It is not recognized as a source of toxins or any potentially harmful compounds, and would be a safe addition to an ornamental pond.

Is Floating Water Plantain Edible? Will Fish Eat it?

Floating water plantain is not necessarily known for its edibility, as there appears to be no apparent records of its use as a food source across its native range. Some of its close cousins in the Alismataceae family are known for being edible, though are not widely incorporated into specific dishes and diets. As the plant produces herbaceous leaves, it is likely that some pond fish may be curious enough to pick at it. However, dense fish populations are recorded to have been present in ponds where it is grown (such as the Dombes pond system in France), with no notable impact on the plant’s survival.

Where to Buy Floating Water Plantain & Seeds? (UK & US)

Luronium natans can be purchased as bare-root or potted plants from plant nurseries or aquascaping shops across its native range. It can also be purchased through online portals of plant stores. Do keep in mind that this plant looks similar to other water plantain species. Make sure to check for the appropriate scientific name when making a purchase. Additionally, ensure that you are purchasing this plant from reputable establishments, particularly in areas where it is protected under local laws.

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