Microsorum pteropus on lava stone.

Microsorum pteropus is a water fern from Asia, 15-30 cm tall. To be grown on a root or stone, attached with fishing line until it has gained a hold. If planted in the bottom, do not cover the rhizome because it will rot.
Easy to propagate by splitting the horizontal rhizome. A hardy plant that grows in all conditions. The black spots under the leaves are sporangia (reproductive organs), not signs of disease, as many believe.