We mowed over it a couple of times last year, so it never bloomed. I've been expectantly waiting this year and it finally came out:
I was expecting an iris, since the leaves look a lot like iris. The blooms aren't very big, the whole thing would fit in the palm of my hand (I have small hands).
Don't deadhead as the seed pods look like blackberries (hence the name), so they give winter interest and then you also get baby blackberry lilies in the spring.