This grower is sure of this plant identification.
Grown from seed and about 2 foot high now - about to flower - grows well here in sunny well drained areas. Looks great en masse and bees love it.
Purple top verbena, South American vervain, Tall verbena, Vervain
Verbena bonariensis (Purple top verbena). This is a tall perennial, which is grown as an annual, and produces deep purple flowers from mid summer to early autumn. The deeply toothed leaves cluster in a mounded rosette.
They are marginally frost hardy to frost tender. Grow them in medium, well-drained soil in full sun or at most partial-shade.
Walls, rock garden, attracts bees and butterflies.