Hi Michael,
Black BG's are a very subjective choice......but in some cases I do like it and this one works for me. I think a little lean to the plant and a bit more of a peek into the lilly would help a bit compositionally as now it is quite centered.
I'd slice a bit off the bottom - just below where you lose all detail in the stem. I do love the way it all melts away into nothingness and those two bottom side petals are so nicely lit!
I do like the flower but I agree that there seems to be a bit too much stem (for me) in this image. Also while I sometimes like a black background, I find myself looking for some color in the background here.
The think I like most about this image is its successful play of color and dark in a high contrast shooting situation. Nice job in tough lighting! I agree the crop can favor this image more, but I'm fine with the vertical stem on this one since you have good negative space to support the bloom (but I often like more negative space than others do)