Cylindricfruit Primrose-Willow

A true red stem plant does not get much redder than this. Ludwigia glandulosa keeps its deep reddish-purple colour even at moderate nitrate levels, which is unusual among red plants — most of them fade to orange or green unless nitrate is held very low. It comes from wetlands across the southeastern United States, where it grows both submerged and emersed.

In the aquarium the stems grow strictly upright and hardly branch on their own. To get a bushy shape the central shoot has to be cut, which forces lateral growth. Even then it stays more columnar than most stem plants, and that upright habit is what makes it work as an accent plant in Dutch-style arrangements or along the midground.

It needs strong light and stable iron dosing. Under weak light the lower leaves drop quickly — the plant does not tolerate shade. CO₂ injection helps but is not strictly necessary, though without it growth slows and the colour intensity drops. It does best at 22 to 25 °C and pH 5 to 7 in soft water.

In the trade it is often mislabelled as "Ludwigia perennis" or the trade name "Ludwigia peruensis". Genuine L. perennis is an Old World species and not the same plant at all. Propagation is by cuttings: trim a stem, remove the lower leaves, and replant. Seeds are also possible when the emersed form flowers.