Aponogeton is a genus of 45 - 50 species of flowering plants, the only genus of the family Aponogetonaceae. The Aponogetonaceae is considered to be allied to the Potamogetonaceae - Najadaceae complex of families.
Individual plants are not always easy to identify due to hybridization (particularly those sold as A. crispus - which are often cultivated hybrids with A. natans).
Generally an Aponogeton from Asia will have a single bloom, while those from African heritage (including Madagascar) will have multiple blooms on the same flower stalk.
They are fully aquatic herbaceous plants with milky sap, becoming dormant during drought conditions. Most species grow from tubers. Most Asian species remain submerged all year round, whilst the starchy tubercles of the African species are able to survive the dry season by shedding their leaves and undergoing a dormant period.
Most are relatively easy to grow in cultivation except the notorious Madagascar Lace Plant (A. madagascarensis )
The African species in particular (with the exception of A. rigidifolius that has a rhizome and not a tuber) experience a natural rest period, corresponding to their habitat drying out in the wild. The Asian species may also have a rest period, but this is temperature related.
As the plant stops growing it can be taken out of the pond or aquarium and put in a bowl of damp sand. Keep the bowl in a dark, cool place with the sand kept damp for approximately 2 - 3 months at a temperature of about 50 - 64F (10 - 18C) until small leaves are seen to sprout from the tuber when they can be returned to the pond or aquarium to grow away again.