Hi,
I have to ramble a bit. I'm sorry. This is a very huge topic.
Umm, so "there's no difference between Virginia and burley" is true and not true. They are (mostly) the same species. So it's not like either grapes or that other thing people smoke, where they are mostly multi-species hybrids.
Nicotiana tabacum, and Nicotiana rustica are both tetraploid, so that is a source of a great amount of phenotypic variation. I'm neither a geneticist, nor a mathematician, but I think it would take both to fully understand the implications for expression.
The terminology we use (burley, bright, oriental) is related to genetics, nonetheless. The thousands of burleys are more closely related to each other than they are to the hundreds of bright tobacco strains, (and vice versa).
The names are related to market classes, and are regulated in many countries, such as by the USDA in America, and they generally overlap with what we logically perceive as significant differences in their qualities. The classes make a lot of sense if you look at one country, then it starts to get muddled if you look too far, (or even back in time).
For example, Indonesia has a classes like sun cured, and rajangan, (a sub category of sun cured), as well as cigar classes with Dutch names that are related to the time of year one plants them.
In India, they have flue-cured, burley, oriental, cigar filler, and wrapper, but they also have groups such as chewing tobacco, hookah tobacco, bidi tobacco, motihari tobacco, natu tobacco, and cheroot tobacco. Cheroot tobacco is all very similar looking and distinct, with long skinny leaves. They are clearly related, but hookah and chew contain both N. tabacum and N. rustica strains. This illustrates the fact that their nomenclature is based on practical use, rather than genetics, but is sometimes the intersection of both.
So, I take an international perspective and try to let everyone call it what they will.
This is
my fuzzy interpretation of tobacco classification in Western countries:
flue cured is straight forward.
Then you've got a broad class of
air cured tobacco. Within air cured tobacco, there are divisions for
light air cured, dark air cured, and
fire cured. Under light air cured, you have
burley, and
maryland. Under dark air cured, you have
dark air, cigar filler, and
cigar wrapper.
So there
are genetic differences. They aren't species level differences. The strains within a market class are (probably) closely related.
Another thing. There are clearly different groups of oriental strains. I have little understanding of it, but the reality is easy to see based on flavour, and leaf and plant size. Bursa is definitely distantly related to Izmir for example. Latakia is not a strain but is made with an oriental, I believe of the
basma classification. If you look at posts in some other forum written by
istanbulin, you will learn lots on orientals.
One more thing. We ought to stop saying turkish as a general term because there are orientals from turkey and there are orientals from other countries. For example, prilep, kavala, mahalla, dubec, and shirazi are examples of important orientals not from Turkey.
Edit:
Another thing to throw into the mix is Delgold, a Canadian Virginia, actually is a multi species hybrid with both tabacum and rustica genes. But we still call it a flue cured strain.