A photo wold help. But here is some info from my profile of the species.
The plant grows leaves--or more correctly, fronds, since it is a fern--and roots from a stem called a rhizome; this must never be buried or it will rot. Black cotton thread may be used to initially affix the rhizome to a piece of wood or rock, and the roots will attach the plant securely. The fronds will grow between 6 and 12 inches depending upon available nutrients. Liquid fertilizer should be added to the water.
This plant assimilates nutrients from the water via the fronds and the roots; black areas on the fronds is a sign of nitrogen deficiency (ammonium). Areas of transparency in the fronds means the plant is receiving too much light. This plant does very well under subdued and diffused light, such as a canopy of floating plants. The plant grows slowly, and older fronds that become tattered and blackened may be removed.