This grower is sure of this plant identification.
Self sprouted seedlings of verbena have been growing in my garden for a few months. they vary between 20-40cm high, and are just beginning to flower. Can swap up to 15 seedlings.
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.