Glad you found it, my girlfriend was there today buying some other plants. They had lots of parrot feather there, and lillies.
Our took some time to open up, and after a few hour finally opened up. It closes when the sun goes down, and then opens back up when the sun hits it in the morning. Yea, they will open in cloudy, but mostly in the sun. It will spread out and grow all around your pond. We just love this plant. It is attracting honey bees however, not sure what that is about. Never seen them before. We bought some Penny Wort too, and thought it was cool.
Yea, there are a couple of guys at that shop that really know their plants. It is in a bad area, but really a neat little place. I think they also build ponds too. Did you get to see their Koi?