Marsilea hirsuta – the ideal foreground plant

by Troels Andersen and Oliver Knott

Marsilea hirsuta is well suited to create a low and dense, green cover in the foreground of the aquarium. This plant is only a few centimetres tall, it grows slowly and it is easy to keep, also for the beginner since Marsilea hirsuta thrives even at very low light. For the expert, the many green colours and the dense carpet are presenting the tank in a beautiful way adding a sense of depth in the aquarium.
 
The scientific name for Marsilea hirsuta(010) is yet to be resolved although it has been commercially cultivated for decades. Tropica first produced this plant back in the early 1980s but it never attained widespread popularity. However, since 2000 the interest in Marsilea hirsuta has dramatically increased and today, this plant is very popular amongst aquarist.
Marsilea hirsuta is a water fern belonging to the Marsileaceae family named after the 18th century Italian botanist G. Marsili. It originates from Australia but today, the genus Marsilea is virtually a cosmopolitan. We have often observed the genus in its natural habitats, for example in Asia, and here, it is usually the species Marsilea quadrifolia that occurs. Apart from Marsilea quadrifolia, Marsilea drummondii is also easily confused with Marsilea hirsuta. In its natural habitat, it is often found emergent where it produces longer petioles and divided leaves resembling clover. This is in contrast to the water form, which has much shorter petioles and whole leaves or leaves which are only divided into two or three lobes.

In Tropica, Marsilea hirsuta is also grown emergent and hence, it is usually supplied with light green clover-like leaves, which after some time under water are replaced by various other leaf forms. The water form can produce whole leaves which resemble a large Glossostigma but it may also set leaves which are divided into two, three or four lobes of different colours and stature depending on the actual growth conditions.
When Marsilea hirsuta is planted into the aquarium, you have to remove the old emergent leaves; these leaves will never adapt to the underwater environment anyway and thus, they only serve to absorb vital carbohydrates from the plant during the transition period to underwater life. From the base, new leaves are set which initially resemble the emergent leaves and which may be divided. Later, however, larger and undivided leaves are produced. From time to time, Marsilea hirsuta produces leaves with longer petioles and these may be removed if they disturb the desired picture of the foreground carpet. The pot should be divided into four to six portions with a scissor and the small blocks may then be planted into the substrate 3-4 cm apart by using tweezers. The plant will spend the initial days producing new roots and subsequently new underwater leaves will also be formed. Thus, Marsilea hirsuta is yet another example of a foreground plant which to begin with does not look too impressive, but which after some time transforms into a dense green carpet.

Marsilea hirsuta tolerates a wide spectrum of light and CO2 conditions and it grows well in soft as well as hard water in a wide pH interval. Without CO2 and at low light, the growth of Marsilea hirsuta almost ceases, whereas it really thrives at moderate CO2 fertilization at a pH around 7. Marsilea hirsuta grows best between 20-26 degrees C and longer periods with higher temperature will often damage the plant. 

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