It is not known exactly which species we grow. We find various names in the literature and on the internet: among others M. angustifolia in Aman’s books, M. hirsuta on Tropica [1], M. crenata most often in shops (although Ch. Kasselmann [2] claims that this species looks different). In fact, the genus Marsilea has more than 60 species, and several are cultivated, especially Australian ones. I am sure that often different species appear in shops under the wrong names, but that is just an aside.
This plant is one of the youngest in my aquariums. I have only been growing it for a few months, but in that short time it has become one of my favorites. Not only because of the fact that it is classed among ferns (you can see tubers at the roots, or a form of rhizome, and the new leaves often grow twisted, just like ferns) – which can always add a touch of mysticism to a natural aquarium – but also because of its use. It is predestined to establish low growth in the foreground of the aquarium. Only Glossostigma elatinoides or Hemianthus callitrichoides can compete with its low stature; I am not familiar with other plants designed to form compact carpets of such low stature. But already here I must single out the great advantage of the marsilea: namely, its lower care and maintenance requirements compared to the previous plants.
When we buy it, we may be surprised by the shape of the leaves (four-leaf clover) and sometimes by their height, often around 15 cm. This is its emerse form. Once planted in an aquarium, it undergoes a considerable transformation. The leaves become smaller, the quatrefoils become three-, two- and single-leaved. Over time, I have established the formation of exclusively single-leaved leaves – the plant produces crawling leaves that pierce the substrate, and small round petals come to the surface, which are very reminiscent of the aforementioned Glossostigma elatinoides. In contrast, however, the formation of horizontal creepers is 100 %, with petals of a deep light green colour forming at regular short intervals. They are firm, almost leathery (unlike the fragile ‘glossa’). Even old leaves retain their shape and rich colouring; I have not noticed excessive curling of old leaves. The originally emerse large leaves will die back over time, we can also help them with scissors. The new leaves are 0,5 to 2 cm tall in my case.
When establishing a front low stand, be aware that Marsilea sp. grows more slowly than most carpet plants and we will never achieve as dense a stand as with species such as Glossostigma elationoides or Hemianthus callitrichoides. It needs a little more planning before planting, or it needs better patience in waiting. Plant in fine substrate cut pieces 2-3 cm long with tweezers so that the rhizome is under the substrate and only the leaves stick out. There will always be a bit of substrate showing through and fast spreading carpet plants will need to be removed (as long as they are in the same tank together, as is the case with mine), such as Echinodorus tenellus, Eleocharis acicularis, Monosolenium tenerum, or even Java moss and Christmas moss. These would eventually crowd out or shade out the marsilea, which would be a shame.
The reward is the beautiful appearance of the plant and its still rare appearance in our aquariums. I would also like to emphasise its maintenance-free nature – there is no need to prune it, it will not happen that for unknown reasons it suddenly starts to grow vertically and stretch towards the surface. It doesn’t have as high a demand for light as its competitors, so it grows nicely and compactly even in semi-shade. It does not spread uncontrollably and does not crowd out other plants. I would describe its fertiliser requirements as standard, and I have not noticed any deficiencies in certain nutrients – more sensitive plants signal these much earlier. These qualities make it a suitable plant for beginner nature-acquarists or aquascapers. They avoid possible frustration. In addition, the plant is perfectly suited for even the smallest tanks.
[1] http://www.tropica.com
[2] Kasselmann Ch. (1999): Aquarienpflanzen. Ulmer, 504 pp.