Source: Magness et al. 1971
As a Vegetable:
Black mustard is in general similar to white mustard in growth and appearance. The leaves are compound pinnate, and hairy. The seed pods are short and glabrous. Black Mustard is little cultivated in the U.S., but is a common weed and young leaves are sometimes gathered and used as pot herbs. The condiment mustard is mainly the ground seed or "flour" made from the seeds of this species.
As a Condiment/Spice:
The condiment mustards of commerce are the ground seeds of these plants, mainly with the seed coats removed. The seeds are near round, 0.1 inch or less in diameter, and produced in pods, which are removed by threshing. Black mustard seed is yellow inside and is the kind of major commercial production.
Production in the U.S.(spice): 15,256,000 pounds, 1959 census. A similar quantity is imported.
Use(spice): As flavoring for meats, pickles, etc.
Part of plant utilized(spice): Ground seed, mainly with seed coat removed.