Phyllanthus fluitans

This nice little floating plant originates from the American tropics and is traditionally counted among the spurge family (Euphorbiaceae). Recent research has shown, though, that the genus Phyllanthus better be placed in its own family, that of Phyllanthaceae.
Phyllanthus fluitans looks pretty similar to a floating fern of the genus Salvinia, however, instead of two floating leaves it has just one on each node (alternate leaves).
The thin submerges stem has tufts of red roots and round, water-repellent floating leaves with a heart-shaped base that hide the stem more or less completely. The leaves often possess a convex centre, whereas the leaf margin is even with the waterline.
Under favourable conditions, tiny white flowers with six petals appear in the leaf axils.

Leaf colour depends very much on light intensity - the more intensive the light, the deeper the brown-red hue the leaves get. It has been observed to do well in hard water when the light is intensive (i.e. full sun outside), whereas softer water (approx. 7° dGH) is better if the light is weaker (B. Wallach).
Like other floating plants, P. fluitans needs ample macro- and micronutrients for healthy growth.
Emersed cultivation is also possible, then the substrate needs to be wet and rich in nutrients (e.g. loam).

Propagation is very easy, like in Salvinia species, too. The plants branch out readily and the floating population divides easily into parts as the stems are quite fragile.