What is the "black seed" mentioned in the Prophet's Hadith: is it black cumin or a bitter-tasting hard black seed?

Black seed is Nigella Sativa, also called black cumin, Indian cumin, or "Habbat al-Barakah" (the blessed seed). It grows in the Mediterranean basin and can reach a height of 50 cm. Its scientific name is Nigella Sativa, and it is a short plant belonging to the fennel and anise family. Its fruit contains white seeds that turn black when exposed to air.