The story of mariamman is quite interesting.
There was a rishi. His wife RenukaDevi is well known for her chastity.Due to the power of her chastiy,she was able to make pots from sand in the river bank and she used to fetch water in that sand pot.
One day when she was fetching water,she attracted a Gandharvan who admired her beauty.This became a black spot in her chastity and the pot started dissolving in the water.
Her husband cursed her for losing her chastity by attracting a Gandharva.He ordered his son parasurama to take of Renuka Devi's head.
Parasuram who is also his father's student accepted his order and went to kill his mother.But renukadevi din't want to make her son to kill his own mother.So she decided to commit suicide.She was rescued by a butcher and a fisherman family.At last Parasurama caught her and cut her head from her body.Also he cut the head of the fisherman and his wife who tried to rescue Renukadevi.
Then he went to his father.He was pleased by his son's obedience and offered him a boon.Parasurama asked his father to wake his mother and the other two.He asked to join the body and head of the victims.Parasuma in an excitation,changed the head of his mother and the fisherman's wife.
Thus the body of RenukaDevi was changed(Maariyadhu) and she became Mariamman.
