This postcard is from an excellent series of showing interesting plants. Each card also has a stamp on the face and an interesting cancel featuring the same plant. I have two cards from this series and the Mandrake is the only one I can identify.
Mandrake or Mandragora belong to the nightshades family. Because their curious bifurcations cause them to have a resemblance to the human figure, their roots have long been used in magic rituals.