Marsilea is a genus of water ferns containing approximately 65 difference species of water clovers, belonging to Marsileaceae, the water fern family. Due to most of our readers hailing from the United States and the United Kingdom, for the purposes of this article we will focus primarily on Marsilea vestita and Marsilea quadrifolia.
Commonly known as hairy water clover (so named for its spore pods that are covered in trichomes, which resemble tiny hairs) and European water clover, respectively, both make excellent additions to ponds. M. vestita is native to much of the United States, while M. quadrifolia is native to central and eastern Europe as well as China and Japan.
Though water clovers look, of course, like clovers, they are in fact pteridophytes just as ferns are. Pteridophytes are among some of the most prehistoric plants, completely lacking flowers and seeds and instead reproducing by releasing spores and extending tough rhizomes.
The spore pods (sporocarps) are fed on by a variety of waterfowl, as they provide fiber and some vitamins, while the plant’s leaves and rhizome mats provide shelter for fish from predators and the sun. The green peach aphid, an avid destroyer of crops and all manner of plants, depends specifically on M. quadrifolia during the summer months.
Water Clover Growth, Hardiness & Climate
Water clovers are fast growers, with vestita and quadrifolia ranging between 4 inches and one foot of maximum height, depending on water depth and sunlight availability. Their rhizomes allow them to spread as much as a meter, generating new shoots as they go. This can make them an intrusive pest in your garden pond if you don’t keep them trimmed back. Stems will rise until they reach the surface of the water, whereupon they’ll spread out their leaves.
Marsilea species do best in hardiness zones 9 and above. However, they will also do just find in as low as hardiness zone 5, as their rhizomes are able to overwinter. Full sun suits them best, but they’ll grow just fine in partial shade as well. These aren’t picky plants, so sandy, loamy, and clay soils all support water clover growth.
The spores from these plants are able to survive in dormancy for decades, but once conditions are right the sporocarps will break open and release new spores, giving quick rise to new plants.
How to Plant Water Clover In Ponds
The growth and care of M. vestita and M. quadrifolia are much the same. They should be planted in water that is at least a few inches in depth. They can either be weighed down, or buried in just enough aquatic planting soil or substrate to cover their rhizomes. Regardless, it is advised that you place them in planting pots to prevent their hardy rhizomes and far-reaching leaves from spreading too far and overtaking your pond or invading natural ecosystems. They do well planted marginally along shallow pond edges, or in deeper waters of up to a foot in depth.
How to Care For Water Clover
An easy plant to grow, water clovers don’t need much – some standing water, sunlight, and space to grow. You’ll want to trim the rhizomes and leaves as needed if they begin to spread too far, or else they may choke out your other vegetation. In addition, their leaves can spread far and cover entire pond surfaces, resulting in oxygen depletion and fish deaths in some areas, though this is typically with invasive varieties. As always, be sure to clean any pruned or dropped foliage from the water to maintain healthy water quality for your fish and other pond residents.
You may wish to harvest sporocarps from the plants before they break open, else you may find yourself with far too many water clovers for your liking. The spores are also easily carried on the wind, enabling them to establish themselves in natural wetlands and lakes several miles away. Do your best to not let this plant spread, even if it is a variety that’s native to your area.
How to Winter Water Clover
No particular steps are needed to overwinter water clover. Their rhizomes are strong and able to survive frost and even the ground freezing solid. Though the rest of the plant will die off come winter, the rhizomes and any unopened sporocarps will simply enter a dormant state, giving rise to new plants once spring arrives again.
Is Water Clover Toxic, Poisonous or Invasive?
Marsilea species occur all around the world. Marsilea mutica, for example, is considered only native to Australia, and may have some growing restrictions outside of its home continent. Hairy water clover, Marsilea vestita, is, however, native to much of North America. If you live in the U.K., European water clover (Marsilea quadrifolia) is native to central and eastern Europe as well as much of Asia, and is considered naturalized in the United Kingdom. Marsilea minuta, dwarf water clover, is native throughout much of Africa, Asia, and eastern South America.
With all of the above in mind, be sure to do thorough research on which water clover species you’re getting and whether or not it’s actually legal for you to have it in your area! Both the United States and the United Kingdom have databases that allow you to search for a plant to determine whether or not it’s native in your area.
Water clover seeds (spores and spore pods) are alright for fish to eat. However, their leaves can be high in thiaminase, which results in vitamin B1 deficiencies if too much is consumed. If your fish nibble a little on the leaves here and there, they should be fine, but be sure to remove any dead or trimmed leaves from the pond immediately just to be safe. The risk is highest during spring, when water clovers are achieving peak growth and pumping out compounds like thiaminase. Summer and fall yield significantly lower thiaminase levels in Marsilea species.
Is Water Clover Edible? Will Fish Eat it?
Historically, some aboriginal peoples in Australia ate the sporocarps from M. mutica, Australian water clover. Another Australian species, M. drummondii (commonly called nardoo), contains a thiamine-destroying enzyme, thiaminase, that has resulted in brain damage as well as death in sheep and horses.
However, aboriginal peoples have eaten it in small amounts seemingly without issue for hundreds of years. The caveat to this is that native peoples learned not to harvest it during the growing season, when thiaminase is the most concentrated. It seems that the sheep and horses affected had eaten the plant in very large quantities during peak growing times, resulting in a build-up of thiaminase in their systems.
As mentioned above, pond fish may nibble on water clover here and there. A bit of foraging shouldn’t harm them, but do your best to keep trimmed or dropped foliage out of the pond, and discourage fish from feeding on these plants during the spring when thiaminase levels are highest.
Where to Buy Water Clover & Seeds? (UK & US)
Water clovers are easily obtained from plant nurseries, pond retailers, and online. However, the most readily available species is M. mutica, which is native only to Australia and is invasive in the U.S. and U.K.
Do not purchase this variety unless you’re located in Australia! Research which species is native where you live, and search specifically for that/those species. Searching by Latin names, rather than common ones, will yield the most accurate results and minimize the risk of obtaining an invasive species.