Limnobium spongia - American frogbit

Hippuris vulgaris is a perennial aquatic plant that is highly decorative, with vigorous growth, and can even be invasive in a pond. However, it is no longer common in France due to the threat to its habitat. It is not often used in domestic ponds, which is a shame because it can be very useful for oxygenating and purifying the water. It flowers in June and July, in the most limited way possible: the flowers, reduced to their bare minimum, are green. The small leaves are a beautiful shade of green.

Hippuris vulgaris belongs to the plantain family. It is a cosmopolitan plant, native to Europe and Asia. The mare's-tail is found in fresh water in ditches, lakes, ponds, and calm rivers. It is a perennial with a horizontal rhizome and tall stems from 20 to 50 cm (8 to 20in) tall, erect, simple, partly aerial, cylindrical, and hollow. The leaves are sessile, linear, entire, and without stipules. The flowers are hermaphroditic, greenish, small, and sessile, appearing in whorls in the axils of the leaves. The fruit is a slightly fleshy, ovoid drupe, about the size of a millet seed. The common mare's-tail develops its leaves in spring, which then die in autumn during frosts. It overwinters at the bottom of the pond in the form of rhizomes.

If the water depth is greater than 60 cm (24in), it is a completely submerged plant. It can develop a significant water plant community composed of a group of flexible, completely aquatic stems. If the depth is less than 60 cm (24in), the tips of the stems protrude from the water, resembling miniature fir trees, bright green and very striking. The leaves are shorter, rounded in section, and much firmer.

Install the Mare's-tail between 5 cm (2in) and 30 cm (12in) of water if you want to enjoy its emergent form. The plant prefers slightly alkaline or calcareous water. Using a container can limit its width in the beginning, but it often ends up growing out of it. This mare's-tail tends to spread a lot, so the solution is to remove a portion of it every year, which is not difficult. This operation helps prevent eutrophication of the pond (excessive nitrates, sediment, etc.). It is a way to balance the ecosystem.

The mare's-tail is an excellent oxygenating plant, with significant ecological value as it is very beneficial to aquatic fauna and less invasive than most others. Its emerging "fir trees" are of great value to aquatic life in general. These zones of exchange between the aerial environment and the water provide a privileged spot for dragonfly molting or amphibian resting. In the submerged part, invertebrates thrive, and fish come to spawn; fry and tadpoles find a safe haven there.

Not producing roots on the green stems, it is much easier to contain within a submerged pot or planter as it only proliferates through its rhizomes. As a nutrient-demanding plant, Mare's-tail also contributes to water purification by assimilating a portion of excessive nutrients: it absorbs a lot of nitrates and phosphates to support its rapid growth. Its withered stems can be used as green fertilizer to spread on another part of the garden.

Etymology of the name Hippuris: derived from Hippos = horse and Oura = tail, alluding to the terrestrial form of the plant.