Mandrakes are the roots of the Mandragora officinarum, a member of the potato family. It is a common plant all over Palestine, growing particularly in the spring and ripening about the time of the wheat harvest.

Mandrake plants

The roots of the Mandragora plant were believed to help in the conception of children. This explains Rachel's interest in the mandrakes that Reuben had found.

Mandrake plant root