Purpletop or Tall Vervain is an upright clump-forming plant with stiff stems and branches.  Flowers are round clusters, 2 to 3 inches across.  Tender perennial. Makes a good cut flower or cottage flower.  Needs full sun and well-drained, fertile soil.  Fairly drought-resistant once established.
 
Start indoors 6-8 weeks before last frost, needs darkness to germinate. Cold stratification may help