Hemianthus callitrichoides is one of the smallest aquarium plants in the world, and creeps over the bottom with millimetre-sized, round leaves. Hemianthus callitrichoides is an attractive and popular foreground plant for small aquariums. 
It is not a difficult plant, but it requires good conditions such as enough light, added CO2, water circulation and fertilizer to thrive. If these conditions are hard to create, you may use Micranthemum ‘Monte-Carlo’ as an alternative, as it is less demanding. 
Small pearls or bubbles of oxygen are often produced on top of the plants, adding a very lively aspect to the carpet.
If planted in small clumps a few centimetres apart, it will spread rapidly and cover the bottom like a carpet. Trim the carpet regularly, otherwise the lower parts will not get enough light causing root death. 
Found on Cuba, west of Havana.