Salvinia Minima

Native to the southeastern United States and parts of Central and South America, Salvinia minima is a small floating fern that sits right at the water surface rather than rooting into substrate. Each plant produces pairs of oval leaves roughly 1 to 2 centimeters across, covered in tiny water-repelling hairs that give them a slightly velvety look and cause water droplets to bead up and roll off.

It spreads by budding off new rosettes, with modified fronds hanging below the surface as root-like structures, and in decent light it can double its coverage in a week or two without becoming the management nightmare that duckweed can be. You can thin it by hand every few days and it stays manageable.

It works well as a surface cover for blackwater setups, breeding tanks, or any aquarium where you want diffused light and a refuge for shy surface-skimming fish or fry. It pairs nicely with low-light species and creates dense shaded patches underneath that some fish really appreciate.

If you search community tank journals online you'll find it showing up in some beautifully natural-looking builds.