Ipomoea aquatica is a semi-aquatic tropical plant grown as a leaf vegetable. Its precise natural distribution is unknown due to extensive cultivation, with the species found throughout the tropical and subtropical regions of the world.
Common names include water spinach, swamp cabbage, water convolvulus, water morning-glory, kangkung (Indonesian, Malay), kangkong (Tagalog), tangkong (Cebuano), kang kung (Sinhalese), pak boong (in Thai: ผักบุ้ง) (Thai), rau muống (Vietnamese), kongxincai (Chinese: 空心菜; pinyin: kōngxīncài; literally “hollow heart vegetable”), home sum choy (Hakka), and ong choy or tung choi (Cantonese pronunciation of 蕹菜, ngônkcôi; pinyin: wéngcài).
Ipomoea aquatica grows in water or on moist soil. Its stems are 2-3 m or more long, hollow, allowing them to float, and these root at the nodes. The leaves vary from sagittate (typical) to lanceolate, 5-15 cm long and 2-8 cm broad. The flowers are trumpet-shaped, 3-5 cm diameter, usually white in color.
In Vietnam, it once served as a staple vegetable of the poor (known as rau muống). In the south, the stems are julienned into thin strips and eaten with many kinds of noodles, and used as a garnish as well. Over the course of time, Ipomoea aquatica has developed into being an ingredient for many daily vegetable dishes of Vietnamese cuisine as a whole. Rau muống is one of the tastes that remind Vietnamese people of their simple and peaceful rural hometown life.
If Vietnam were to declare an official vegetable, I have no doubt that it would be rau muống. Rau muống is served in homes and restaurants across the country and unlike your average nutritious green, this one has no trace of bitterness.
The most popular preparation of rau muống involves boiling them until softened and then sauteeing them in oil and copious amounts of garlic (rau muống xào tỏi). With a squeeze of lemon juice and the addition of tomatoes, the water that the rau muống is boiled in can be served as a bland, but passable soup.
Another reason why rau muống is so popular is because it’s seriously dirt cheap. For 1,000 VND, I took home a huge bundle that was more than enough for two meals.