Plants can be propagating by two ways:
1. Sexual Propagation: Some aquatic plants reproduce themselves through seeds or spores. For example Barclaya longifolia, Aponogeton madagascarinis, Bacopa sp. Etc. These plants need favorable water parameters, proper lighting, and nutrients to produce flowers in the tank. When a plant reproduces a flower, make artificial pollination through a brush of finger. If plant produces seeds successfully, collect and store them to produce new plantlets.
Aponogeton madagascarines flower
Reproducing plant through seeds
I have successfully grown Barclaya longifolia through seeds using following technique.
a. Take a vessel. I had used earthen pot for this purpose.
b. Make a bed of mud/soil of atleast one inch in the vessel.
c. Now put seeds over the soil. Temperature should be around 23 degree celcius.
d. Spray water daily over the soil to keep it wet. Keep away vessal from the reach of birds.
e. After germination of seeds, increase the water level on daily basis according to the height of plantlets.
f. When plants height reach around 2 inch, move them in aquarium.
Barclaya longifolia seeds
Barclaya longifolia cultivation through seeds
Water sprite produces new plants through leaves