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Wu Yu (Eleocharis tubers / Water Chestnuts)

Bitter, sweet, slightly cold, non-toxic. Primarily treats Xiao Ke (wasting-thirst syndrome, characterized by excessive thirst and urination), Bi Re (heat-type Bi syndrome involving joint pain and heat), warms the middle jiao, and benefits qi. Also known as Jie Gu, also known as Shui Ping. Leaves emerge in the second lunar month, resembling taro roots. The rhizomes are harvested on the third day of the third lunar month and sun-dried.

Tao Hongjing states: Currently, Jie Gu grows in paddy fields. The leaves have forks (pronounced like "wu ya"), resembling those of Alisma orientale (Ze Xie), but not exactly like taro. Its rhizome is yellowish like a small taro tuber and can be boiled for consumption. Suspecting that which is called "Wu" has extremely similar rhizomes but is finer and more delicious, while the leaves differ significantly, resembling Amaranthus spinosus (Xian Cao) and being called Ci Ru, it is likely this species. The commentary of the Xin Ben (New Material) states: This herb is also named Cha Ya, and also named Ci Ru (pronounced "gu"). It treats various toxins. For postpartum blood stagnation attacking the heart causing near-death state, difficult labor, or retained placenta, crush and take one sheng of the juice. It grows in water; its leaves resemble arrowheads, belonging to the Alisma category. The Qian Jin Fang states: It treats Shi Lin (lithuria/kidney stones). Minister Yuxi and others, according to Meng Shen, note: Ci Ru should not be eaten in large quantities. People in Wu often eat it, causing them to suffer from Jiao Qi (foot disease/gout). Furthermore, it triggers Hong Jiao Qi (swollen feet), Tan Huan Feng (paralysis/weakness). It damages teeth and causes loss of taste. It can be made into flour for food. It brightens the eyes, stops thirst, and resolves jaundice. If there is pre-existing cold qi in the body, it must not be eaten. It causes abdominal distension and fullness. If children eat it in autumn, pain will occur below the navel.

Ri Hua Zi states: Ci Ru is non-toxic. It eliminates wind toxicity, removes heat from the chest and stomach, treats jaundice, opens the appetite, and promotes digestion. Those taking mineral drugs (Jin Shi Yao) benefit greatly from eating it. He further states: Ci Ru is cold and toxic. Crushed leaves applied externally treat snake and insect bites. Excessive consumption induces deficiency heat, Chang Feng hemorrhoids, metrorrhagia and leukorrhea, and skin sores. Boiling with fresh ginger neutralizes these effects well. Pregnant women should avoid it. It is also known as Yan Wei Cao and Wu Yu.

Tu Jing states: Wu Yu is currently known as Fu Ci. Old texts do not specify its origin province. The shoots resemble dragon's whiskers but are finer, strictly green in color. The rhizome is black, about the thickness of a finger, with thick skin and hairs. There is another variety with thin skin and no hairs, which is also used. People in the fields eat it and also process it into flour; consuming it enriches the gastrointestinal tract and suppresses hunger. It is especially suitable for those taking cinnabar and sulfur pills (Dan Shi), as it can detoxify. Er Ya calls it Shao.

Yan Yi states: Wu Yu is now called Bi Qi (Water Chestnut). Those with thick skin, black color, and hard white flesh are called Zhu Bi Qi (Pig Water Chestnut); those with thin shiny skin, pale purple color, and soft flesh are called Yang Bi Qi (Sheep Water Chestnut). People harvest and eat them in the first and second lunar months. These two types are rarely used in medicinal prescriptions. In years of famine, people collect them to supplement their grain supply.