Latin name: Mentha nemorosa
Other names: Yerba Buena, hierbabuena, Cuban Mint
Yerbabuena is a kind of fragrant Cuban mint, used as a medicinal plant and in food. Medicinally it is apparently good for digestive upsets. It is not clear if this is just ordinary peppermint, or if the local variety is different.
The term is ambigous, since sometimes it is used to refer to ordinary culinary spearmint. Peppermint is menta.
It is an ingredient of the mojito cocktail, though regular mint is usually substituted, since yerbabuena is difficult to obtain except via a Cuban community or a hispanic market.
Yerbabuena, oddly enough is mistranslated by babelfish from Spanish to English as "marijuana". The name just means "good herb" in Spanish, which doesn't necessarily imply dope.
Note that Clinopodium douglasii, which is found in western and northwestern North America, is also referred to as Yerba Buena, but it appears to be otherwise unrelated. It is not a mint, but is used to make Oregon tea.
www.mojitomint.co.uk was a short-lived a site that sold Yerbabuena mint from in New Covent Garden, London, UK, to bars and restaurants for use in the popular Mojito cocktail.
Thanks to Andromache01 and lila for Spanish herbal information.