This is a common weed in Hawaii with a small purple/violet flower that is spreading throughout all the islands.
If not already declared a noxious pest it will undoubtedly reach that status shortly. The citation below gives an interesting commentary on the plant.

"Verbena Jamaicensis (JAMAICA VERVAIN) grows in Jamaica, Barbados, and other West Indian islands, bearing violet flowers.
The juice is used in dropsy and for children as an anthelmintic and cooling cathartic.
The negroes(???)use it as an emmenagogue, and for sore and inflamed eyes.
As a poultice, with wheat-flour, the bruised leaves are used for swelling of the spleen, and for hard tumours at their commencement."

Quoted from
----A MODERN HERBAL----
by Mrs. M Grieve (1931)