Arrowhead/慈菇 is also known as chiku or ngaku. They are edible tubers and found in shallow wetlands.
Above: Arrowhead Chips Recipe
They are usually available only during the Chinese New Year season in Singapore due to their auspicious symbolism. The leaves when sprouted, are tall, up-pointing and resembles an arrowhead, symbolising continuous growth (步步高升). In Singapore, you can buy them from Giant or the wet markets. The tuber has a water content resembling water chestnut, and perish relatively quickly, so use them as soon as possible after purchase.