This I believe is a species of Echinodorus, commonly called sword plants. There are several species with varying leaf shapes and sizes, but the leaves look like swords to me.
If there is a bulb, then it is likely Aponogeton, of which there are several species. I don't know them well enough to suggest which but there are two or three with leaves as here.
Aponogetons need a lot of nutrients otherwise they whither away and die. They grow rapidly for a few months before this happens because they use the nutrients in the bulb. When that runs out they start to rot away. Alot of them also need a rest period after flowering.