This pious tradition comes to us from legends that flowers with tear-drop resemblance sprang up where Mary's tears fell on the ground at the foot of the Cross.
Virginia Spiderwort: blue tear-like fluid from spent blooms
Quaking Grass: tear-like seed clumps
O Jesus, behold the tears of the one who loved Thee most on earth, and who loves Thee most ardently in heaven! Amen+