Crystalwort (Riccia fluitans): floating cover or a cushion on rock

Crystalwort is not a moss but a liverwort: a rootless plant made of small, branching ribbons of bright green that float in masses just below the surface. It has two uses. Floating, it is perfect shelter for fry and shrimp. Tied to a stone under a fine mesh, it forms a striking green cushion on the bottom that, under high light, is covered in oxygen bubbles. That second use takes work: it must be trimmed and re-tied every few weeks, because it grows upwards and comes loose.

---