Black Turmeric (Cucurma caesia) Plant
One well established plant. Not frost hardy! But would probably do well as a potted house plant for the winter in non-tropical climates.
Similar to their more familiar cousin the yellow Turmeric, but more of a bitter flavor and often held in high regard as a medicinal. The inside of the rhizome is sky blue when mature (and fresh) and slowly oxidizes to black.