Is there a difference between Thai lemon basil and lemon basil? I have four lemon basil plants in the backyard, and I found pretty easy to find at several nurseries in Chicago, including Soukal, Meinke, Gethsemane Gardens, and what used to be the Egg Store on Archer and is now under some other name. Early in the season, it seemed like only genovese and lemon basil were available at all the stores. Only later in May did I find my favorite basils: cinnamon and Thai sweet (horapa).
Gethsemane Gardens also stocked two different types of holy basil, but the gardening expert there explained to me that they were Indian varieties of holy basil (tulsi) and were not used culinarily. I tried to research the taxonomy of plants known as "holy basil" and haven't quite reached anything definitive. All types are
Ocimum tenuiflorum, they do seem to have some kind of difference between them, but I haven't been able to find a direct comparison in terms of taste and aroma.