It drives me mildly insane that people think black cardamom is, in some way, a lesser version of green cardamom. That’s the (erroneous) word on the street. But the truth is that they have different flavors and applications, so no spice rivalry is allowed here.
Cardamom, in general, is known for having astringency, a warm, camphorous, palate-clearing flavor. Where green is more pungent and menthol, black cardamom is earthier, less eucalyptus and more lovely, woodsy smokiness; there’s a picture of green cardamom in this post on peaches with cardamom streusel. Green cardamom is used a lot in South Asian desserts, coffee and other sweet stuff; black cardamom works better in savoury applications – added to Indian tandoori marinades and stews and found in Asian soups and vegetable stir fry dishes.
I absolutely love using black cardamom, which is also referred to as brown cardamom (not to be confused with the third type – Thai cardamom…which could be a whole other post). It is fantastic in plain white or brown rice, thrown in whole or split to add a little kick. When the seeds are ground, they make a delicious addition to a barbeque dry rub for chicken, beef or pork, and I also (secretly) throw some in to the braising liquid of my beef short ribs…shhh.
I have yet to see these in a regular grocer (one can only hope), but they can definitely be found in East Asian specialty stores as well as Indian and Middle Eastern grocers.