Jim, The Nymphaea you have referred to is usually Nymphaea lotus (syn. Nymphaea zenkeri) also known as tiger lotus. The tuber is like a hazelnut, a little bigger. Normally the tubers which float are dead, healthy ones fall onto the bottom of the tank and start growing in about 2 weeks when water is around 20°C. The most often sold Aponogentons are the following species: A. bolivianus, A. henkelianus, A. longiplumosus, A. madagascariensis and A. ulvaceus. The latter is the least demanding and is very vigorous, also the tubers are less susceptible to rot. There are also nice assortment of rhizomatous aroids, like Anubias, they sometimes flower under water. There is a company not far from where i work, i visit them a couple of times a year. Aquarists are like bulbophiles, very friendly, helpful and generous! Janos from Hungary