Stiff Verbena (Tuber Vervain, Roadside Vervain)

Scientific Name - Verbena rigida Spreng.
Family - Verbenaceae

Perennial from tubers with erect or ascending four-angled stems. Leaves opposite, lance-shaped with coarsely-toothed margins. Purple to violet flowers in clusters. Reproduces by seed, tuberous roots and rooted stems. Found in the continental United States,west to Texas. Also occurs in Canada, the West Indies and South America. A related species, moss vervain, has a prostrate growth habit, finely divided leaves and lacks rhizomes.