This perennial has upright stiff quadrangular stems and forms a loose clump. The tall stems have sparsely placed mid green lanced-shaped toothed leaves and the small lilac to purple trumpet-shaped flowers appear in a spike from spring to summer. 

Hardiness zones 7 to 10

Verbena bonariensis is naturally found in South America growing in well drained fertile moist sandy to light clay soil in an open sunny position and is drought and frost tolerant.

Purple Top is often known as 'square weed' from its square stems and has naturalised in many countries. It is used in perennial gardens along borders or grown in containers but is normally regarded as a weed and is controlled by physical removal of the plant before it sets seed. If necessary apply glyphosate. ID 820

Verbena (ver-BAY-na) bonariensis (bo-nah-ree-EN-sis)

Verbenaceae (ver-be-NAY-see-ee)
Teaks, Verbenas