This
green vegetable is a favorite in
Chinese cuisine. Its competing
botanical names are
Ipomoea aquatica and
Ipomoea reptans. It has
triangular pointed leaves of a
dark green color, and its
stems are light green and
hollow, hence the name
kong1-xin1 cai4, "empty-heart vegetable". It is sometimes used as a symbol of heartlessness in love-songs.
The leaves and stems are eaten. The root is said to have some medicinal uses - for women's yeast infections, among other things. I can't vouch for that. It has a white or pale red flower, but most Chinese people know it best from the leaves seen at market and on the dinner table.
Another name for it is weng4-cai4, which seems to mean "vat-planted vegetable' (although a different Chinese character with the same sound is generally used). It can grow directly in water without soil, and so is popular for cultivation in poor areas. In some places it is planted between the boards of special rafts that float on ponds and lakes. The English names "water spinach" (independently noded) and "swamp cabbage" are also used for this plant, as is the market name ong choy, which is simply the Cantonese pronunciation of weng4-cai4.
The leaves are soft and cook quickly. It is therefore a favorite of small restaurants that want to save on cooking fuel. It is very tasty, especially when stir-fried with garlic or with fermented bean-curd (see also the recipe for stir-fried parsley).