The flowers themselves aren't going to be that helpful in figuring out which species it is. With the exception of a couple of West Coast species, all the North American Sisyrinchiums have basically similar flowers (some species have a higher proportion of individuals with blue flowers, some have a higher proportion of individuals with white flowers, but all are capable of producing white, blue, or bicolored flowers. S. campestre and S. albidum have 1 to 2 sessile inflorescences per stem while S. atlanticum has 1 to 4 stalked inflorescences per stem. Can't really tell from the pictures whether the inflorescences are sessile or stalked, but there doesn't appear to be more than one inflorescence per stem which leans towards S. campestre or S. albidum. S. campestre and S. albidum or not easy to tell apart. S. albidum USUALLY has two inflorescences at the tip of each stem with three bracts below them. S. campestre USUALLY has just one inflorescence at the tip of each stem with two bracts below it. Usually is the key word there.
