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Rhubarb Rhizoma is the dried root and rhizome of the Polygonaceae plant Rheum palmatum L., Rheum tanguticum Maxim. ex Balf., or Rheum officinale Baill. The first two are commonly referred to as "Northern Rhubarb Rhizoma," while the latter is known as "Southern Rhubarb Rhizoma." Among them, Rheum palmatum and Rheum tanguticum (Northern Rhubarb Rhizoma) are mainly cultivated in provinces and regions such as Gansu, Qinghai, Tibet's Changdu and Nagqu, and Sichuan's Ganzi and Aba. Those produced in Tongren, Tongde, and Guide counties in Qinghai are called "Xining Rhubarb Rhizoma," those from the Qilian Mountains and Wuwei areas in Gansu are called "Liangzhou Rhubarb Rhizoma," and those from Quanshui, Lixian, and Xigu in Gansu are called "Quanshui Rhubarb Rhizoma." Rheum officinale is mainly produced in Sichuan, Guizhou, Yunnan, and Hubei provinces, either cultivated or wild, with relatively lower yield and quality compared to Northern Rhubarb Rhizoma.

Materia medica research suggests that since the Shennong Bencao Jing, the Rhubarb Rhizoma mentioned in literature has almost always been the Rheum genus of the Polygonaceae family, specifically the Rheum palmatum group. However, the specific varieties differ depending on the region of production. Among them, Rheum palmatum and Rheum tanguticum are the mainstream varieties, with Gansu, Qinghai, and northern Sichuan being the traditional and authentic production areas since ancient times.

bubble_chart Varietal Identification

Rhubarb Rhizoma is named for its color. Both Bielu and "Wu Pu" have the alternative name "Huangliang." The "Guangya" states: "Huangliang is Rhubarb Rhizoma." The Shennong Bencao Jing lists it as a lower-grade herb, noting its ability to "cleanse the intestines and stomach, expel the old and bring in the new." It is also known as "General," with Tao Hongjing explaining: "This medicine is extremely potent... the title 'General' is given for its swift and vigorous action." The "Wu Pu materia medica" provides a detailed description of the plant morphology of Rhubarb Rhizoma: "It sprouts in February, with yellow-red leaves arranged in pairs, a yellow stem, and grows to about three feet tall. It blooms yellow in March and bears black fruit in May. The roots are harvested in March, containing yellow sap, cut, and dried in the shade." Tao Hongjing mentions that high-quality Rhubarb Rhizoma has a "purple humifuse euphorbia herb color." Combined with the emphasis on the laxative effects of Rhubarb Rhizoma in materia medica since the Bencao Jing, it is undoubtedly confirmed that this Rhubarb Rhizoma belongs to the Rheum genus of the Polygonaceae family, containing combined anthraquinones that have a contact laxative effect when taken orally. As for the specific sources of early medicinal Rhubarb Rhizoma, it is difficult to pinpoint, but based on regional analysis, the three varieties used today are generally included.

It is noteworthy that the description of the plant morphology of Rhubarb Rhizoma in *Xin Xiu* is quite unconventional. Su Jing stated: "(Rhubarb Rhizoma) leaves and stems resemble those of Japanese dock root (*Rumex japonicus* Houtt.), but are thicker, longer, and more robust. Its roots, when thin, also resemble those of Japanese dock root, while the larger ones are as big as a bowl, measuring two feet in length... In the regions of You and Bing (modern-day Hebei and Shanxi), the roots gradually become thinner, and their potency is inferior to those from Sichuan. Nowadays, it is produced in Dangzhou, Liangzhou, Xiqiang, and Sichuan. Its stems taste sour and can be eaten raw to relieve heat, though excessive consumption is harmful." According to this, Japanese dock root (*Rumex japonicus* Houtt.) belongs to the Polygonaceae family, genus *Rumex*, and its leaf shape differs significantly from the three authentic species of Rhubarb Rhizoma today. Particularly, the text mentions a type of Rhubarb Rhizoma produced in You and Bing (modern-day Hebei and Shanxi), with "sour-tasting stems that can be eaten raw to relieve heat, though excessive consumption is harmful." This is likely the wavy-leaved North China Rhubarb Rhizoma (*Rheum franzenbachii* Münt.) or the He Tao Rhubarb Rhizoma (*Rheum hotaoense* C. Y. Cheng et C. T. Kao), or it might even be a *Rumex* species mistakenly identified by Su Jing. Although Su Jing's understanding may have been incorrect, the Rhubarb Rhizoma used in the Tang Dynasty was primarily from the palm-leaf group of the *Rheum* genus, as evidenced by the records in *Bencao Shiyi*: "When using Rhubarb Rhizoma, its potency should be differentiated. If one seeks a deep, thick, and potent effect for treating diseases, the Sichuan variety resembling ox-tongue slices, which is firm and hard, should be used. If one seeks a swift purgative effect to expel stagnation and remove heat, the Hexi variety with brocade-like patterns should be chosen." The Sichuan variety resembling ox-tongue slices likely corresponds to the modern Southern Rhubarb Rhizoma, which has a relatively mild purgative effect, while the "Hexi brocade-patterned" variety corresponds to the modern Northern Rhubarb Rhizoma, known for its strong purgative properties.

In addition, according to the records in Qianjin Yifang, Rhubarb Rhizoma is produced in three places: Xizhou of Hedong Dao (now Xi County, Shanxi Province), Kuozhou of Longyou Dao (now Guide County, Qinghai Province), and Maozhou of Jiannan Dao (now Maowen, Sichuan Province). Judging from the production areas, the Rhubarb Rhizoma from Kuozhou of Longyou Dao should be what Chen Cang-qi referred to as "the one with brocade patterns from Hexi," which is suspected to be the northern Rhubarb Rhizoma today; the Rhubarb Rhizoma from Maozhou of Jiannan Dao should be what Chen Cang-qi referred to as "the one resembling ox tongue slices from Shu," which is suspected to be the southern Rhubarb Rhizoma today; and the Rhubarb Rhizoma from Xizhou of Hedong Dao should be the North China Rhubarb Rhizoma of the wavy leaf group, as described by Su Jing, similar to Japanese dock root.

The illustrations in the Rhubarb Rhizoma section of Zheng Lei are too simplistic to help determine the species, but among them, the Jia You edition quotes Shu Bencao mentioning Shu Rhubarb Rhizoma: "The leaves resemble castor beans, the roots are like large taro, with fine roots growing beside them like burdock, and the smaller ones also resemble Japanese dock root." It also states: "It grows six to seven feet tall, with brittle stems." (Note: These sentences are quoted by Tang Shen-wei as "Tang Ben says," but it is unclear which is correct.) This should refer to the medicinal Rhubarb Rhizoma Rheum officinale. Bencao Tujing mentions more varieties of Rhubarb Rhizoma. Su Song states: "(Rhubarb Rhizoma) is now found in the prefectures of Shuchuan, Hedong, and Shaanxi. The best is the brocade-patterned one from Shuchuan, followed by the one from Qinlong, known as Tubo Rhubarb Rhizoma. In the first month, it produces green leaves resembling castor beans, with the larger ones as big as fans, and roots like taro, with the larger ones as big as bowls, one to two feet long, with fine roots growing beside them like burdock, and the smaller ones also resembling taro. In the fourth month, it blooms yellow flowers, and some have green or red flowers resembling buckwheat flowers. The stems are green-purple, shaped like bamboo. The roots are harvested in the second and eighth months, the black skin is removed, and they are dried by fire. Additionally, Dingzhou produces a type of Japanese dock root Rhubarb Rhizoma, which is very effective in treating scabies and itching. The initial seedlings and leaves resemble Japanese dock root, and after growing for several years, the leaves resemble pokeberry root but are narrower and sharper. In the fourth month, five to seven stems emerge from the pressed branches, with flowers and leaves of the same color, bearing fruits resembling buckwheat but lighter and smaller, ripening in the fifth month and turning yellow. It is also called wild buckwheat rhizome. The seedlings are harvested in the third month, the fruits are collected and dried in the shade in the fifth month, and the roots are harvested in the ninth month. When broken, they also have brocade patterns, and after sun-drying, they are also called dock root."

In the text, the one with leaves resembling castor beans and blooming yellow flowers should be the previously mentioned Shu Rhubarb Rhizoma, i.e., the medicinal Rhubarb Rhizoma Rheum officinale, while the one with green flowers resembling buckwheat flowers is the palm-leaf Rhubarb Rhizoma Rheum palmatum and the Tangut Rhubarb Rhizoma Rheum tanguticum. As for the Japanese dock root Rhubarb Rhizoma from Dingzhou (now Changde City, Hunan Province), it belongs to the Rumex genus. It is worth mentioning that in the Southern Song Dynasty, Wang Jie's Lyuchanyan Bencao mentions Sichuan Rhubarb Rhizoma, stating: "It is cool in nature and slightly toxic. For major medical swelling and toxicity, regardless of the amount, crush it and apply it to the affected area." However, according to its medicinal illustration, it does not resemble the Rheum genus at all. Mr. Zheng Jinsheng identified it as dock root Rumex madaio Mak., which should be correct.

Subsequently, mainstream materia medica from the Ming and Qing dynasties, such as Pin Hui Jing Yao, Bencao Mengquan, Bencao Gangmu, and Zhiwu Mingshi Tukao, all recorded Rhubarb Rhizoma consistent with the three authentic types used today. Among them, the illustration in Tu Kao (Figure 1) shows leaf shapes closer to the palm-leaf Rhubarb Rhizoma.

bubble_chart Historical Evolution of Authentic Production Areas

In the early days, there were two types of Rhubarb Rhizoma origins, northern and southern. The "Wu Pu Materia Medica" states: "Some grow in the northern part of Shu Commandery, and some in Longxi." It is suspected that those growing in the northern part of Shu Commandery are the southern Rhubarb Rhizoma of today, which is the medicinal type of Rhubarb Rhizoma, while those from Longxi are the northern Rhubarb Rhizoma. The "Mingyi Bielu" only mentions the northern Rhubarb Rhizoma: "It grows in the valleys of Hexi and Longxi." Additionally, the "Shui Jing Zhu" (Commentary on the Water Classic), Volume 13, in the note on the Luo River, quotes the "Wei Tudi Ji" (Records of the Wei Territory): "Fifty li east of Dai City is Mount Daola, where excellent Rhubarb Rhizoma grows." This, along with the earlier mention in the "Qianjin Yifang" that Rhubarb Rhizoma is produced in Xizhou of the Hedong Circuit, and the Sichuan Rhubarb Rhizoma in the "Lyuchanyan Bencao," could either be the wavy-leaf group of Rhubarb Rhizoma or plants of the Rumex genus, none of which are the genuine Rhubarb Rhizoma, and thus need not be discussed.

As for the superiority of the northern and southern types of Rhubarb Rhizoma, there has been considerable divergence throughout history. Bencao Jing Jizhu states: "Nowadays, those collected from the northern part of Yizhou, Wenshan, and the western mountains, although not from Hexi or Longxi, the good ones still exhibit a purple humifuse euphorbia herb color, with a very bitter and astringent taste, and a deep black color." Tao Hong-jing's statement implies that the high-quality Rhubarb Rhizoma produced in Sichuan can barely match that from the northwest, indicating that Sichuan's product is deficient compared to Hexi. The opinion in Xin Xiu is exactly antagonistic, with Su Jing stating: "Tao's claim that Sichuan's product is deficient compared to Longxi is mistaken." However, Su Jing's view is not absolute, as previously cited Chen Cang-qi's perspective suggests that both types of Rhubarb Rhizoma have their uses, but if measured by their purgative effects, the Hexi brocade-patterned ones are clearly stronger than the Sichuan ox-tongue-shaped ones. The Song dynasty's Su Song shares the same view as Xin Xiu, believing that the Sichuan brocade-patterned ones are superior to those from Qin and Long, as cited earlier.

Until the Ming and Qing dynasties, opinions on the superiority of northern and southern Rhubarb Rhizoma were still divided into two factions. Bencao Mengquan states: "Shaped like an ox tongue, produced in Sichuan, it must be heavy, solid, and brocade-patterned; do not use light, loose, or rotten black ones." Bencao Gangmu, however, says: "Nowadays, people consider those from Zhuanglang to be the best, Zhuanglang being the ancient Jingyuan Longxi area, which aligns with Bielu," thus considering the Rhubarb Rhizoma produced in today's Gansu Zhuanglang as the best. Zhiwu Mingshi Tukao states: "Nowadays, those produced in Sichuan are considered good," and The Identification of Medicinal Production states: "The highest quality is produced in Wenchuan and Guanxian in Sichuan, and Xing'an and Hanzhong in Shaanxi."

Combining the study of species changes and the evolution of production areas, it is recommended that the southern Rhubarb Rhizoma (medicinal Rhubarb Rhizoma) be considered as originating from Sichuan as the authentic production area, while the northern Rhubarb Rhizoma (Rheum palmatum, Rheum tanguticum) should be considered as originating from Gansu and Qinghai as the authentic production areas.