Whorled Pennywort

Hydrocotyle verticillata, known in trade as the whorled pennywort, grows wild in the warmer regions of the Americas, where it prefers very moist soils and also stands in shallow water. In the aquarium it stays low and creeping. Its runners travel along the substrate and form a dense carpet, and the round leaves that rise from them bring to mind small parasols. Planted in open foreground space, the effect is a soft green mat.

The plant is more demanding than its plain appearance suggests. It is rated difficult, with an optimum temperature of 18 to 25 °C with a pH of 5 to 7.5; it survives cooler and warmer water. Growth is fast once established. Height tracks light intensity: under stronger light the plant stays low and compact, while dimmer conditions make it stretch upward. Carbon dioxide injection is beneficial to its growth. A balanced supply of nutrients is all the plant needs; generous dosing makes the dwarf form that hobbyists covet give way to much larger leaves. Propagation is easy by runners, cuttings, or splitting the clump. When kept emersed in moist soil it grows well out of the tank as well.