It's a floating fern. I would try for something larger and sturdier, such as water lettuce, if you want the frogs to be able to climb onto it. Salvinia would work well to fill the spaces in between the larger plants, though, and will help with water quality.
Each plant is usually about 3-6" across. You could get two or three; they will divide and spread (like most floaters), so you'll need to thin them out periodically. You can usually find them at pond suppliers, and sometimes at Lowes or Home Depot.
keep an eye on them for the next few days and see if you can tell a difference in one from the other. Such as location of a certain spot, if 2 spots merged into one, or if one has a slightly different color than the other. Then you can see if they are both males if they both croak or if one's a male and the other is a female. There should be 1 males per 2 females to increase the chances of breeding succesfuly.
Males only make a low pitched squeek that sounds like a dog crying. (You'll know what it sounds like when you hear it.) And Females make a chittering sound like a squirrel.
For some people, it's very easy to breed them because they lay eggs all the time. But other people, (Like me) only see their FBTs "getting happy" but not any eggs. If you see them doing the do, don't get too excited because sometimes they don't lay any eggs and the female slips away. But you still have to wait about 1-2 years if you got them from Petsmart or Petco. They have to be 3-4 years old to reach sexual maturity and when they sell them they are usually 2 years old.