Verbena bonariensis, Tall vervain is a rapidly growing, erect, clump forming perennial herb. The 3-6 ft. (0.9-1.8 m) tall stems are slender, hirsute, rough and square. Upright stems branch widely off the central stem. V. bonariensis may survive as an annual in colder climates as it readily self-seeds.
Foliage
Leaves of V. bonariensis are dark green. Most of the leaves are in a basal rosette. The stem leaves are opposite and the base of the leaf clasps the stem. Leaves are elliptic to lanceolate, ranging from 3-5 in. (7.6-12.7 cm) long with serrate margins.
Flowers
The small five petaled flowers of V. bonariensis are lavender to purple and are borne in cymes. They bloom all summer until the first frost.
Fruit
V. bonariensis fruits are nutlets. Each flower produces four seeds.
Ecological Threat
V. bonariensis is native to South America. It has escaped cultivation and become naturalized in disturbed areas across the southeastern United States and in California. It is drought and heat tolerant and is very common along roadsides and other disturbed areas. V. bonariensis is very similar to V. montevidensis and V. incompta and all three are invasive species.