Marsilea is a type of aquatic fern commonly known as water clover. It also has been referred to as pepperwort or nardoo. This fern is of the Marsileaceae family and has 70 worldwide. It is named for Count Luigi Ferdinando Marsigli (1656-1730), an Italian botanist.
Marsilea is often confused with Trifolium, the clover found growing in grassy areas. Their appearance is similar, but the Marsilea always has four leaflets, which are wedge-shaped and might be smooth or covered with fine hairs. These green leaflets grow 1 to 1.5 inches (2.5 to 3.5 cm) wide. The plant grows vigorously and can become invasive.
The perennial water fern grows underwater, rooted by a hairy, narrow rhizome that allows it to spread, or creep. Leaves grow along the rhizome, with long, slender petioles growing upright. Oval, brown spore cases, the size of peppercorns, form at the base of these stems. A four-part leaflet develops at the top of each petiole. After the stem breaks the surface of still water, leaflets float on top.
Water ferns are native to shallow areas of fresh water and are often found growing in lakes, rivers, ponds and swamps where sunlight or light shade is prevalent. They need warm temperatures to thrive. Marsilea can be found in many countries across the globe, but it is most prominent in Australia and Africa. In some areas, such as Asia, where it grows in rice fields, the water fern is considered a weed and poses a severe problem.
Marsilea is desired as an ornamental plant for aquariums and in gardens where aquatic plants are the focus. It can be planted directly into mud at the bottom of a pond or started indoors in a pot, then transferred to underwater soil. This type of fern adapts best to a potting medium of equal parts loam, sand and peat moss. In its natural habitat, the water fern will withstand long dry periods, using the drought as a resting phase. In cultivation, pots should be placed in shallow containers of water to maintain moisture levels.
These types of ferns are known for their ability to reproduce by a method known as alternation of generations. This is a continual process of alternating between sexual and asexual reproduction. In the sexual reproductive stage, cells divide, forming eggs and sperm, each with its own genetic code. The egg and sperm combine to make a new plant. In its next reproductive cycle, Marsilea forms single cells that develop spores, which grow into plants with the same genetic plan.