Azolla caroliniana

Azolla caroliniana is a tiny floating water fern native to the Americas that carries within its leaves a symbiotic cyanobacterium (Anabaena azollae) capable of fixing atmospheric nitrogen — a unique trait that gives it natural fertilising properties. Under low light it remains green, but under bright light the fronds develop vivid red and orange tones, creating a spectacular fiery surface display. It spreads rapidly and is valued both as a shade provider and as a nitrogen-fixing biofertiliser in planted systems.