Star fruit, so named because it has five prominent ridges that make it star-shaped on cross section, is the yellow- or green-skinned fruit of the carambola(ゴレンシ)tree. Because it contains high levels of oxalic acid(シュウ酸), it is typically sour and its juice can be used to remove stains from clothing. Like grapefruit, star fruit possesses compounds that make it dangerous to consume when taking certain medications, including those used to treat heart conditions.