I can't see the pics, but it is probably purple loosestrife. It wouldn't be for sale because it is illegal to sell in most states due to being an extremely invasive weed.

It is not purple loosestrife. I don't know what it is but I know it isn't loosestrife.

Could it be Caryopteris Blue Mist? It is a shrub.

Thanx for the replies guys. I looked at some pictures of both and it didn't exactly looked like either, the foliage resembles that of the loosestrife but the flowers of the caryopteris. Is there more that one variety of loosestrife, I'm going to do a little research on it.

It is not a member of the loosestrife family at all. There are many varieties of loosestrife but only purple loosestrife is a noxious weed. My first guess was it is in the mint family based on the flowers but it doesn't have a square stem. I think I will look further. It is a curious plant.

The flowers do look like caryopteris but the foliage is way different and caryopteris would never tolerate being grown in water.

Is it this?? Wild mint?? See photos at--
http://www.google.com/search?q=wild+mint&hl=en&client=firefox-a&rls=org.mozilla:en-US:official&channel=s&biw=1211&bih=610&prmd=ivnse&tbm=isch&tbo=u&source=univ&sa=X&ei=9gA2TtPLJYPd0QHa5aj_Cw&sqi=2&ved=0CCYQsAQ

The flowers do look very much alike , but the leafs are more narrow on my plant than on that of mint, when I first saw it I thought it was some sort of mint but upon closer inspection I realized it wasn't

The flowers look similar but the leaves are much different. Nice try though.

What the heck kind of pond store doesn't know the name of a plant in their own display????