Katmon (Dillenia philippinensis), locally called bolobayaua, belongs to a family of flowering plants that grown in low to medium altitude forests. The tree is endemic to the Philippines and it can be found on Babuyan Islands, Luzon, Polillo, Mindoro, Masbate, Leyte, Negros Island, Guimaras, Cebu and Basilan.
It grows on an evergreen tree that grows as tall as 15 meters. Its trunk is erect and the bark is smooth with shallow fissures. The leaves are leathery, shiny and oblong in shape, measuring 12 to 25 centimeters long, and coarsely toothed at the edges. Its flowers are white, large, showy, and about 15 centimeters in diameter with reddish pistils and stamens. The edible fruits are round, about six to eight centimeters in diameter, with large fleshy sepals tightly enclosing the true fruit. Its fruit is also known as elephant apple. A red dye is also obtained from the bark of this tree.
Katmon fruits are quite fleshy, eaten when green and have a taste similar to green sour apples. The fresh fruit is not especially flavorful, but due to its acidity and juiciness, it is refreshing when eaten. It makes an excellent sauce or jam and is also used for flavoring. For example, it may be added to pinakbet (a traditional Philippine vegetable and pork dish) or sinigang (traditional Philippine fish, pork or vegetable sour soup) as a souring ingredient. Locals are also known to mix the acidic fruit juice with sugar into a drink taken to treat coughs and fevers, and the young leaves or bark may be pounded into a paste applied to wounds or swellings.
The katmon fruit is not usually found for commercial sale, and is instead harvested for personal use. The trees are propagated by seed, but are currently threatened as they are often cut down for timber. The species is currently considered threatened. If lost, a traditional flavor of the Philippines and an important component of the local culinary tradition will be lost as well.