Better known in Taiwan and southern China as 莲雾 (liánwù) — 洋蒲桃 is the more formal botanical name. The fruit is bell-shaped, pink to deep red, with a light apple-pear flavor. Native to Southeast Asia, it's a staple of Taiwanese fruit stalls.
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Don't confuse with 葡萄 (pútao, grape). 蒲桃 (pútáo, rose apple) and 葡萄 (pútao, grape) are homophones in casual speech but written with different first characters — 蒲 is a marsh plant, 葡 is reserved for grapes.