Micranthemum, or also “Baby’s Tears” as our ocean aquarium colleagues call these plants – either because of the shape of the leaves or because of their tendency to “bubble” easily, i.e. to form “droplets” of oxygen that resemble little tears.
Both Micranthemum umbrosum and Micranthemoides are native to North America. Both species are mudflats and inhabit the banks of streams and rivers that typically have neutral or acidic pH and not very high temperatures.
In their native habitats, they form dense, low clumps that look somewhat like lawns.
It is not difficult to distinguish the two members of the genus from each other: the opposite leaves are larger and more rounded in umbrosum, smaller and more elongated in micranthemoides.
In the aquarium
As with all mud plants, the bottom plays a key role in successful cultivation.
Clay substrates and inert fine gravel with enriched substrate are ideal in this case, although after about 6-8 months it may be advisable to add a tablet fertiliser. Continuous addition of potassium, which is taken up by the leaves, then facilitates and encourages uptake of macro-nutrients from the bottom.
Plants of the genus Micranthemum are very susceptible to chlorosis, which is evident as discoloured areas on the leaves. The risk of this occurring is minimised by adding microelements (primarily iron). If we want to grow both species successfully, strong lighting is necessary.
In my experience, Micranthemum micranthemoides suffers at higher temperatures (above 26 °C), while umbrosum seems to be quite tolerant of elevated temperatures. Both species – and again especially micranthemoides – are very sensitive to chemicals in algaecides and some pharmaceuticals.
Reproduction of the plants occurs by means of lateral buds: on the thin stems, at each individual node, new branches develop, which quickly thicken the shrub. However, this thickening causes a noticeable loss of light reaching the lower parts. As a consequence, yellowing and dropping of the lower leaves can occur if we do not intervene in time by regular trimming or by pulling the whole shrub out of the substrate, dividing it into several parts and then planting it in different places in the aquarium.
Due to its versatile use in the aquarium, Micranthemum is very popular among aquarists. It is well suited as a solo plant protagonist in small aquariums; it will do us an excellent service in creating contrasting shrubs if planted next to plants with a different shade or shape of leaves; it is ideal for forming “steps” and alleys between roots and rocks.
In my layouts, I prefer to place Micranthemum in the middle ground, usually so that it covers the base of the roots as they rise towards the surface. Or I let these plants peek out from behind rocks while covering the bases of tall plants at the back of the aquarium. I consider it inappropriate to use these species as “turf” species, as this way of growing them completely suppresses their “personality” or typical growth habit.