According to Metro of 17 January 2013, pentagon-shaped iyokan (Citrus x iyo) fruits, produced in Yawatahama, Japan, are being marketed as good-luck charms for students taking exams.
Plant-Lore
Collecting the folklore and uses of plants
DISCLAIMER: The cures and other uses on this site are recorded as they were received.No attempt has been made to evaluate them; so anyone tempted to use any of them does so entirely at their own risk.