Verbena n. : A genus of herbaceous plants of which several species are extensively cultivated for the great beauty of their flowers; vervain.

Example:
Where can I buy lemon Verbena leaves?

Taxonomy
Verbena, Moldenke, Vervain, species, Briq, intermedia, Cham, Kunth, Phil, Common Vervain, M. Perry, plants, genus, family Verbenaceae, Hayek, free encyclopedia, Ruiz, Glandularia.

Defination from the web:
Verbena as well as the related mock vervains (Glandularia) evolved from the assemblage provisionally treated under the genus name ... For some vervain pathogens, see List of verbena diseases. ...