All around the neighborhood, including in many sidewalk strips, are clumps of a different kind of iris. They flower later, seem to last longer, and have thinner leaves and smaller flowers than the purple kind I'm used to, and almost all are mostly white. I can't figure out what kind they are because Wikipedia informs me iris types are primarily defined by what you see when you dig up the plants.

( A few more photos back here. )

( A few more photos back here. )