As you can see, these plants really have nothing to do with poppies, which have four petals. These three-petalled flowers are more closely (though not very closely) related to lilies.
They grow easily from seed, but the seedlings will surprise you. Juvenile, underwater leaves are strap-shaped, so you might think that you are looking at a different plant!
Water popiesand revert to the underwater straps of their childhood.
In colder situations they are likely to behave as annuals. They are also less ornamental. All of them have a tendency to produce some underwater buds which never open, but have the curious ability (known as cleistogamy) to produce seed without being needing to be fertilised by insects. In colder climates, the plants produce more of these cleistogamous flowers, and fewer, if any, chasmogamous ones. (This lovely word just means the ordinary kind of flower with petals!) You might be excused for thinking that they are not flowering at all.
They like their water to be nitrogen-rich, and are a bit touchy about pH, preferring it to be under 6.2, (so might not thrive on our black soil which is more alkaline).