blue waterhyssop

Crushed leaves of Bacopa caroliniana give off a lemon scent, which is one of the plant's most distinctive traits. It comes from the southern and central United States and Mexico, where it grows in marshes both under water and above it, and it has been kept in aquariums for many years.

The ovate leaves wrap their bases all the way around the stem. Stems reach 10 to 60 cm and branch readily from the base. Several forms are in cultivation, among them a smaller-leaved one and a variegated one that looks much like the standard plant.

It is undemanding and slow enough to need little attention, which makes it a good first stem plant. Medium to strong light supports cultivation; added CO₂ and a balanced nutrient supply can improve growth. Lamp wattage per litre alone does not establish the light reaching the plant. Its optimum is 20 to 25 °C at pH 5 to 7.5. Strong light combined with little nitrate turns the leaves bronze or brownish, and a shortage of phosphate gives them a slight pink tint.

Take cuttings from the tips or side shoots, or cut off the runners that form at the base of the stems and replant them. A stepped group in the midground, or in the foreground of a larger tank, gives neighbouring plants something to build around. In a temperate summer it can also be grown emersed at the edge of a pond, where it grows fast with a creeping habit, hairy stems and purple flowers.