For all intents and purposes, all pipe tobaccos are based on three different families- Virginia, Oriental and Burley. A great many different sub-species and variations on these primary "Varietals" exist.
Oriental leaf (sometimes referred to as "Turkish") is somewhat enigmatic in it's role in finished tobacco blends. Some call it a "Condimental" or "Spice" tobacco, the purpose of which is to add a certain flavor and body to a blend. Others have utilized it a "Base" tobacco accounting for a greater portion of the blend.
In any case, Orientals are characterized by what many have described as an herbal, earthy flavor with both sweet and piquant undertones. It has been described as being "Aromatic" but I would call it "Odoriferous". It kinda' has a sharp stinky bag aroma, and good oriental tobacco has a room note reminiscent of stale flatulence. (Hey, I'm entitled to say what others are thinking!) Since Social Justice Warriors in the early '90s made tobacco their cause d'jour it has become impossible to get fine Turkish cigarettes in this country ( Regie Turque, Balkan Sobranie and Fatima that come to mind) you could always tell if someone was burning them by their distinct nasty room note....delicious, but you aren't going to win friends and influence people by smoking straight Turkish tobacco.
The Oriental tobacco plant is characterized by it's dwarf size and multitude of small leaves, Typically "Sun Cured" this tobacco takes on different color and taste characteristics depending on the soil in the region it is grown. Oriental Varietals are named after the places in which theay are grown: Xanthi, Basma, Yenidje, Drama etc....all cities which were from the same region during the Ottoman Empire.
All of this is moot to the USA blender, because Oriental varietals are all bought up by big cigarette companies. What's left over is mixed together and sold to pipe tobacco companies as "Blended Turkish Ribbon". The exception is "Izmir", a lighter colored milder flavored Oriental leaf that is often, for reasons I don't know, available in the USA.
The Orientals available to small blenders today come mainly from Sutliff Tobacco in the form of their TS19 Turkish and their TS24 Blended Turkish Ribbon. Cornell and Diehl used to be a source for pure Izmir tobacco, but I don't know if they still offer it...
Next Up....my favorite: Burley!