Called “holy herb,” from its use in ancient sacred rites. Also called “pigeons' grass,” “Juno's tears,” and “simpler's joy.” Supposed to cure scrofula, the bite of rabid animals, to arrest the diffusion of poison, to avert antipathies, to conciliate friendships, and to be a pledge of mutual good faith; hence it was anciently worn by heralds and ambassadors. (See Roodselken.)
Verbena is the botanical name.
“The term Verbena (quasi herbena) originally denoted all those
herbs that were held sacred on account of their being employed in the
rites of sacrifice.” —
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Vervain from Fact Monster: