If I am not mistaken, the picture from the Plant Finder (needs a better name IMVHO :mrgreen is of the regular Lobelia cardinalis, which is many times larger than the dwarf variety. Aside from the size difference, L. cardinalis 'Small Form' has oval leaves while the regular variety has elliptical leaves.
Although extremely easy to grow IME, one thing of note is that this plant will literally melt if you happen to overdose K relatively to some-other-nutrient(s)-that-I-have-not-been-able-to-figure-out (suspecting Ca/Mg but who knows). Growing this plant emersed is also not difficult: shade to medium sun. Unlike Sue, my emersed specimens don't really care about moisture. I have two pots of the dwarf variety outside right now that I haven't water in weeks and they are still strong, showing no signs of wilting and the leaves are purple. You should try growing yours submersed Sue before looters dig yours away in the middle of the night.
Here is a picture of my L. cardinalis 'Small Form':