Water shield is a kind of perennial water plants. Originally, it grows wild in the lakes and ponds south to the Yantze river, especially in Taihu Lake and West Lake of Hangzhou. The leaves of water shield are oval and dark green. The back of the leaves can secrete agar-like mucilage, which possesses abundant protein, dextrose, etc. The water shield can be made boiled or fried. It is not only a kind of vegetable with distinct flavor but also functions to clear away heat, nourish the lung and stomach, smooth the urine, promote the subsidence of swelling, remove the toxic materials and cease diarrhoea.

There has been manual cultivation of water shield since the last years of Ming dynasty. The water field grows very fast. The roots start to sprout around the Pure Brightness festival every year and the tender leaves picked at this time are called “ spring water shield”. After the Beginning of Summer, the temperature increases and the water shield grows well. Around the 18th solar term, it is the time to pick water shield in large quantities, which is then called “autumn water shield”. At present, there are groves of water shields in the fields in the East Hill. The vast expanse of water shields seem to embellish Taihu Lake with a beautiful green lace, exhibiting a picturesque scenery.

The water shield can be eaten fresh. Besides, it can be preserved, bottled or tinned for long-term preservation or for exportation. Taihu Lake water shield does not only sells well in domestic markets. It has also won the title of “ Foreign Trade Product of Fine Quality” and has good overseas markets. Seasoned with other spices, Taihu Lake water shield can be made into delicious dishes such as “watershield soup with shrimps”, “watershield with lotus”, etc. They are listed among the famous suzhou cuisines and have been in an increasing demand in the hotels and restaurants.

What ' s more, Taihu Lake watershield is also a symbol of homesickness. As recorded in classical documents, there was once an official named Zhang Han who resigned from his office in the north when he thought of the watershield. This is how the saying “ Watershield-stimulated homesickness” came into existence.