gladiolus x colvillei

I have no idea what this flower is. (edit: it's a Gladiolus x colvillei)

This is a single stem. Looking at a bloom face on, there are three larger petals at the top, three smaller ones below, each pointed at the end, coming from a deep base. The blooms are about two inches wide when fully open, and are a clean white. The leaves are iris-like. Any ideas?

toyo 45cf, 101mm wollensak raptar lens, 4x5" ilford FP4+ film, f64, 8 second exposure, natural light