As the post for verbena pointed out, Spanish has invested that Latin word with two meanings: ‘a certain type of flowering plant’ and ‘a kind of festival.’ If English shares only the first of those senses, it compensates by having a second version of the word that finds no counterpart in Spanish. English acquired its doublet vervain from verveine, the form that Latin verbena had developed to in Old French. Which of the two words English uses, verbena or vervain, seems largely arbitrary.
E. Cobham Brewer, writing in his Dictionary of Phrase and Fable in 1898, said that vervain is “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.” Then he stepped back onto terra firma and added that verbena is the botanical name for the plant.
I’ll add that the plant that botanists call Verbena halei is known colloquially as Texas vervain, a name that identifies one state where the plant grows abundantly. Another vernacular name is slender vervain; the description is accurate, as the following photograph—taken in a rainier springtime than the current one—of this delicate plant with small violet-colored flowers confirms.
© 2011 Steven Schwartzman