Piedmont primrose-willow

The narrow leaves taper to a fine point and turn orange-red under strong light, which makes this Ludwigia one of the better choices for a red accent in smaller tanks. Ludwigia arcuata is native to wetlands across the southeastern United States, where it grows emersed as easily as it does submerged.

The stems are thin and branch readily when trimmed. Each leaf is about 2 to 3 cm long and arranged in opposite pairs. Under moderate light the plant stays green and grows at a steady pace, but under high light the top portions turn a reddish-orange while the lower leaves may drop if shaded by upper growth.

It needs CO₂ injection to stay compact and keep its lower leaves. Without CO₂ the stems grow spindly and the internodes stretch, giving the plant a thin, drawn-out look. The optimum temperature is 24 to 26 °C (FG optimum), and soft, acidic water at pH 4.5 to 7 suits it best. It tolerates a wider range but colour and density suffer.

Propagation is by cuttings — trim a stem, remove the lower leaves, and replant. It grows fast enough that regular trimming is needed once established. The cut stems can be replanted in the same group to keep the clump dense. It also grows emersed, producing small yellow flowers above the waterline.