Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Lamiales
Family: Verbenaceae
Genus: Verbena

Verbena is a genus of about 250 species of annual and perennial herbaceous or semi-woody flowering plants. The majority of the species are native to the Americas and Asia. Their leaves are usually opposite, simple, and in many species hairy, often densely so. The flowers are small, with five petals, and borne in dense spikes. Typically some shade of blue, they may also be white, pink, or purple, especially in hybrids.
In New Zealand, some species and their hybrids have escaped cultivation and are growing wild.

Photos below are of a hybrid growing wild on the banks of the Waitangi River, Northland.
1-Verbena hybrid.jpg 

1-Verbena hybrid-002.JPG

1-Verbena hybrid-001.JPG

The square stem
1-Verbena hybrid-003.JPG

1-Verbena hybrid-004.JPG

The leaf's underside.
1-Verbena hybrid-005.JPG

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0