Sorting Out the Basils (Ocimum)

I have read the Q&A about basils but I have an additional one. I am doing research work and am quite puzzled by the varieties and I am trying to sort out the differences between Ocimum canum, Ocimum caryophyllatum, Ocimum sanctum. My research has to do with homeopthic preparations and if there are distinguishing botanical features between them, it would be most helpful. Will you be able to help me out or direct me to an excellent resource?

Years ago Helen Darrah attempted to classify the cultivated varieties of basil. Her book, "The Cultivated Basils" published by T.E. Thomas Buckeye Printing Company in Independence, Missouri, in 1980, is almost certainly out-of-print now. In any case, its focus is at the species level and I have heard from botanists that it is sorely out-of-date or incomplete. Indeed, we have not used it much in recent years ourselves because of various shortcomings that we have noticed.
Thomas Debaggio and Susan Belsinger published a book, "Basil: An Herb Lover's Guide" which is still in print (and available from Richters). It is not intended to be anything more than what its title suggests: a basil lover's guide. But it has excellent photos and covers many obscure varieties that are not described anywhere else.
As for a currently accepted taxonomic key to the genus, Ocimum, I do not know if any such thing exists today. It is my impression that the genus is need of a through revision. But you should contact Dr. Arthur Tucker at Delaware State College who is a specialist in commercially important herbs including basils and who probably can advise you further if there is anything reliable available today.