Hi Rita,
Frogbit and Azolla are teeny tiny floaters. They can reproduce well.
Floating hearts and Snowflakes are plants that you plant in a pot, but keep under the water just a bit, but they put up leaves that float.
I've tried Parrots feather both ways, and I think it does better potted up.
Here's a pic of my azolla from several years ago. It forms a really solid mass. (Can you see the baby frog on the leaf?). I really like azolla.
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I like the azolla too. That is what really quickly cleared up my green water last year. Haven't tried the frogbit yet but want to. Am looking forward to plants being available at the pond store. They said it won't be for another month. Too cold yet.

I was able to find Red Stemmed Parrots Feather locally all potted up already so bought it. I like it.

I also bought four bunches of Hornwort at the local pond store. Thursday they will have Anacharis so I intend to get that too. I just threw the Hornwort into the pond loose and its on the bottom.

I doubt they will have any frogbit but we will see.