Adventive from farther south in moist (usually) to dry cultivated gardens and fields, ditches, dumps, and disturbed places (e.g., construction sites). First collected in 1861 in La Crosse.

The flowers, including the calyx and anthers, are generally small, but parts are somewhat variable in size. Sometimes treated as P. pubescens Porter & J. M. Coult. var. grisea Waterf., but most recent authors follow Martínez (1998) in accepting P. grisea, as well as P. pruinosa L., as distinct species.