Cardinal Flower

Cardinal flower is a North American marsh plant that the aquarium trade keeps in a submersed form for the midground. In the garden and along wet ditches it grows tall and sends up spikes of scarlet flowers, which is where the common name comes from; submersed in a tank it stays a neat, low stem plant with elliptical leaves arranged along an upright stem.

It grows by cuttings, and the stems root readily when re-planted, so a single plant becomes a group without much effort. The leaf colour shifts with light and nutrients: bright green under moderate light, with a reddish cast on the undersides when light and iron are generous. It is undemanding about water chemistry within a pH of 6 to 7.5.

Temperatures of 22 to 26 °C suit it best, with tolerance in either direction. CO₂ is not required, but a planted tank with injected CO₂ keeps the growth denser and the leaves more uniform. It also grows emersed readily on damp substrate, which makes it one of the easier plants to multiply in quantity before flooding the aquarium.