What plant is that?

The mystery plant for February 2022 is an introduced perennial. It’s white flowers (½–¾” across and about 1” long) have deeply cleft petals that often trick the unwary into miscounting them. The calyx is enlarged and appears inflated. The plant produces large panicles of these flowers and grows to around 2 feet tall. The entire plant is smooth with alternate, entire gray-green leaves. It grows in dry places and open fields.