Lilywort

The name causes most of the confusion around this plant. Ricciocarpos natans sits in the same division as Riccia fluitans and gets sold under overlapping common names, but the two behave nothing alike. Riccia forms submerged tangled mats that need tying down; Ricciocarpos floats at the surface as discrete rosettes and stays there.

Each rosette is a fan-shaped, slightly cupped thallus with a central groove and a purple underside carrying long ventral scales. It is a liverwort, so there are no true roots, leaves or stems anywhere on it. Rhizoids trailing from the underside take nutrients directly from the water column, which makes a decent surface population useful for soaking up nitrate in a heavily stocked tank.

In practice it grows quickly in cool, bright, still water and sulks in warm turbulent water, where the thalli go pale and break apart. Around 18 to 26 °C and pH 5 to 7.5 suits it. It needs no CO2 and no substrate. What it does need is a calm surface, so it is a poor match for open tanks running strong flow or a skimmer.

It is hardy enough to overwinter outdoors in sheltered ponds across much of Europe, which makes it one of the few surface plants that will hold in an unheated tank. New rosettes bud at the margins of mature ones and detach without intervention.