The dark color stems in your photo remind me of Chocolate Mint,but I would be wrong. According to this site (which is not a plant site) the best Yerbabuena used for Mojitos has dark stems and is grown in Cuba; the stem is what imparts the best flavor to the Mojito. http://cookmundo.com/page/2/ Some say that Mojito Mint is Mentha x vollosa.
Sunset Zone 28, AHS Heat Zone 9, USDA zone 8b~"Leaf of Faith"
