These batwan fruits are used as souring agents in Ilonggo cuisine.
Whereas the non-Visayans of the Philippines commonly use tamarind and even kamias and guavas to sour their sinigang, the Ilonggos use batwan.
Also spelled batuan.
Scientific name: Garcinia binucao
Batwan trees can be found all over the Western Visayas regions, particularly the two Negros provinces and Iloilo.
Have never tried using these… because they’re simply not seen outside the Visayas.