B. nigra

B. nigra may refer to:


 * Ballota nigra, a perennial herb of the family Lamiaceae
 * Betula nigra, a species of birch native to the eastern United States from New Hampshire west to southern Minnesota, and south to northern Florida and east Texas
 * Brassica nigra, the black mustard, an annual weedy plant cultivated for its seeds, which are commonly used as a spice