Lemon tree very pretty
And the lemon flower is sweet,
But the fruit of the poor lemon
Is impossible to eat.

With a sort of calypso lilt

Harry Belafonte, late Fifties?

Edit:
Nope: "Lemon Tree is the ninth (9th) song on the Peter, Paul, & Mary album and the third (3rd) song on the Ten Years Together album. It is an original song by Peter, Paul, And Mary."

Google strikes again.