Lobelia cardinalis

Lobelia cardinalis is a North American wildflower that has been widely adopted in the planted aquarium hobby in its compact aquatic form. The round, spoon-shaped leaves are bright apple-green on the upper surface and a striking violet-purple on the underside — a contrast that becomes especially dramatic when light passes through the leaves from above. It grows at a slow to moderate pace and stays compact at 10–20 cm, suiting tanks from 40 litres upward. It is grown as a rosette-like stem plant, and trimming the top encourages bushy side branching over time.

Light: Medium (30–55 PAR); the violet undersides intensify under brighter lighting. CO2: Beneficial; CO2 injection improves growth rate and leaf colouration significantly. Fertiliser: Root tabs or substrate fertiliser; liquid fertiliser weekly with potassium and iron. Planting: Midground; plant singly or in groups of 3–5 stems 3–4 cm apart; suitable for smaller tanks. Growth: Slow; reaches 10–20 cm; pinch tops to encourage compact, bushy form; cuttings root readily.