There are about 250 species of annuals, perennials, and sub-shrubs in the Verbena genus. Most are American natives with square stems, opposite leaves on the stems, and small flowers in clusters or spires. Usually the flowers are purple, pink, scarlet, or magenta.
Plants in this genus like full sun to part shade and sharp drainage and tolerate drought and heat. Deadhead to encourage re-bloom and propagate by division or cuttings or seed.
I would not be without Verbena bonariensis in my garden. It's an annual, but it attracts birds, butterflies, and hummingbirds over a long season in zones 7-10. It self-seeds happily in my zone 5 garden and likes sun, and my local herd of deer don't bother it.
Grown mainly as an annual also, Verbena canadensis is a native with a trailing habit and dark purplish-pink flowers in zones 5-10. Useful in containers and hanging baskets, Verbena hybrids such as ‘Homestead Purple', ‘Sissinghurst', and ‘Patio Blue' and ‘Patio Purple' have intense color and heat and disease resistance in zones 9-10. Be restrained with the fertilizer, however, or you will get more leaves than flowers.
In zones 9-11, Verbena peruviana will creep around in your garden beds, and ‘Red Cascade' is an especially vibrant color.