Cavendish is not a plant or tobacco varietal:  it is the name for (most commonly) Virginia and Burley tobaccos which have been put through a specific curing process and storing/cutting method.  After their respective curing process, (Burley: air-cured, Virginia: flue-cured), Cavendish tobaccos are steamed, usually with sugars or flavoring in the water, in order to infuse the tobacco with moisture and a subtle sweetness.  After steaming, the tobacco is stored under pressure (pressed) for an additional curing/fermentation period.  Pressing can last from a few days to several weeks and flavorings and/or casing can be added at any stage throughout the process.  The color and flavor of the Cavendish will vary between natural and black, depending on what flavoring is added and how vigorous the pressing is.