ID btw. Cassia bicapsularis and Senna pendula var. glabrata

I purchased a Cassia from a local nursery this week - per the grower, it will reach approximately 12-20' at maturity, depending on conditions. He did not know the scientific name, and now I'm in a conumdrum as I do not want to plant it if it's the invasive type I found in my internet research. I do believe , based on what I saw in full bloom at the nursery, that it is likely one of these two: Cassia bicapsularis (http://davesgarden.com/guides/pf/go/1328/) or Senna pendula var. glabrata (http://davesgarden.com/guides/pf/go/142452/). Could also be Cassia fistula (http://davesgarden.com/guides/pf/go/38312/). There were 3 plants in the same 5 gal pot (all from grafts), so I've divided them and am currently recovering them - photo is of the largest baby (quite stressed from the root trauma).

I do not have seed pods available at this time, since I purchased an immature plant not yet at blooming size - I know seed pods are a way to differentiate. I believe it is the non-invasive C. bicapularis since he gets new plants by grafts or rooting, not through easy re-seeding.

Essentially, my question is whether anyone knows how I can positively ID the plant as the non-invasive without a seed pod?

Here are some of the sites I found:
http://floridagardener.com/pom/cassiabicapsularis.htm
http://florida.plantatlas.usf.edu/Plant.aspx?id=1331
http://florida.plantatlas.usf.edu/Excluded.aspx?id=522
http://www.tytyga.com/product/cassia+tree

Leaves don't look like C. fistula, and I also see flower buds on it and it's supposed to be a spring bloomer so I'd rule that one out. S. pendula var glabrata is listed as blooming in mid-summer so it might be a bit late for it to be blooming too. Leaves look right for C. bicapsularis and this is the right time of year for it to start blooming, and it's widely available in the trade whereas S. pendula var glabrata is not, so if I had to put money on something I'd bet on C. bicapsularis. But I couldn't say 100% for sure.

Thank you for the input, ecrane3!!! It's actualy blooming right now here in central FL, but apparently just started. There are a couple of flower buds on the one I bought, though not many since it's small, and wilted since I just stessed it.

Here is what's hopefully a better photo of the immature flower buds.

Emma