John Calvin Commentary Genesis 30:14

"And Reuben went in the days of wheat harvest, and found mandrakes in the field, and brought them unto his mother Leah. Then Rachel said to Leah, Give me, I pray thee, of thy son`s mandrakes." — Genesis 30:14 (ASV)

And Reuben went in the days of wheat harvest. This account of the fact that a boy brought home I do not know what kind of fruit from the fields, and presented it to his mother, by which she purchased from her sister one night with her husband, has the appearance of being trivial and puerile.

Yet it contains a useful instruction. For we know how foolishly the Jews glory in extolling the origin of their own nation: for they scarcely deign to acknowledge that they have sprung from Adam and Noah with the rest of mankind. And certainly, they do excel in the dignity of their ancestors, as Paul testifies (Romans 9:5), but they do not acknowledge this as coming from God. Therefore, the Spirit purposely aimed at beating down this arrogance when he described their race as sprung from a beginning so mean and abject. For he does not here erect a splendid stage on which they may exhibit themselves; but he humbles them and exalts the grace of God, since he had brought forth his Church out of nothing.

Regarding the kind of fruit mentioned, I have nothing certain to adduce. That it was fragrant is gathered from Song of Solomon 7:13, and while all translate it mandrakes, I do not contend on that point.