The Marblemelon is harvested from the Marblemelon Plant. It can be found inside Marguerit's Greenhouse in small pots. The Marblemelon is a small growable flora. There is also a smaller variant, it takes less space and gains less food and H2O.
Due to the high amount of food, H2O, and energy it gives, the Marblemelon Plant is an all around excellent plant to farm.