Hornwort

Hornwort is a rootless aquatic plant native to every continent except Antarctica, which tells you a lot about how tough it is. Underwater it forms long, bristly stems covered in whorls of stiff, needle-like leaves that give it a distinctly prehistoric look.

It doesn't anchor with roots, so it floats freely or can be loosely weighted at the base if you want it standing upright in the background. Either way it grows fast, sometimes alarmingly so, pulling nitrates and ammonia out of the water column at a pace that makes it genuinely useful rather than just decorative.

In a heavily stocked tank or a fry setup, a few bunches of hornwort can be the difference between stable and chaotic water chemistry. It also provides dense, tangled cover that small fry, shrimp, and shy fish seem to appreciate.

New arrivals often shed needles for a week or two while adjusting to your water, which looks alarming but usually resolves on its own. Check out journal threads from planted breeding tanks to see how people actually use it.