Pittsburghers usualy call it “phlox,” but this ubiquitous late-spring flower is really a member of the mustard or crucifer family, as you can tell by the four-petaled flowers (real Phlox flowers have five petals). It came from Europe as a garden flower and quickly made itself at home. It would be hard to conjure up any inhospitable feelings toward this welcome guest, whose bright flowers decorate roadsides and back yards everywhere (these flowers were blooming in Mount Lebanon in late May). Each colony blooms in a mixture of colors from deep magenta to white, and many plants grow flowers with splashes or stripes of contrasting colors.
Gray describes the genus and the species:
HESPERIS [Tourn.] L. ROCKET
Pod linear, nearly cylindrical; stigma lobed, erect. Seeds in 1 row in each cell, oblong, marginless. Cotyledons incumbent. Biennial or perennial, with serrate sessile or petiolate leaves, and large purple flowers. (Name from hespera, evening, from the evening fragrance of the flowers.)
H. MATRONALIS L. (DAME’S VIOLET.) Tall: leaves lanceolate, acuminate; pods 5-10 cm. long, spreading. Sometimes cultivated, and spreading to roadsides, etc. (Introd. from Eu.)