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Dyers Woad is the dried leaf of Isatis indigotica Fort. of the Brassicaceae family, Isatis Root is the dried root of Isatis indigotica Fort. of the Brassicaceae family, strobilanthes root is the dried rhizome and root of Baphicacanthus cusia (Nees) Bremek. of the creeping rostellularia herb family, and Indigo is the dried powder or mass obtained from the processed leaves or stems of Baphicacanthus cusia (Nees) Bremek. of the creeping rostellularia herb family, Polygonum tinctorium Ait. of the Polygonaceae family, or Isatis indigotica Fort. of the Brassicaceae family. Isatis indigotica is mainly produced in Dingxian and Anguo in Hebei, Suqian, Rugao, Taixian, and Gaoyou in Jiangsu, Taihe, Linquan, Bozhou, and Huaiyuan in Anhui, Dancheng in Henan, and Huoxian and Lanxian in Shanxi. Generally, those produced in Rugao, Jiangsu and Anguo, Hebei are considered authentic. Baphicacanthus cusia is mainly produced in Xianyou, Fujian, Jiangyou, Shifang, and Jiangjin in Sichuan, and also in Hunan, Zhejiang, Guangdong, Guangxi, and Yunnan. Indigo is an artificial product, mainly produced in Fujian, Hebei, Yunnan, and Anhui, with Fujian being famous for its production, known as "Jian Indigo".

Materia medica research suggests that the drug "Lanshi" in Bencao Jing should be the fruit of Polygonum tinctorium of the Polygonaceae family, and until the Song Dynasty, Polygonum tinctorium was still an important source of medicinal "Lanshi". However, starting from the Song Dynasty, the medicinal parts of "Lan" changed, with prescriptions using roots gradually increasing. The name "Isatis Root" appeared in Song and Yuan medical prescriptions, and it is suspected to be a colloquial writing of "Ban indigowoad root", referring to the root of "Da Lan" or "Ma Lan", with its authentic sources mainly being today's Isatis indigotica and Baphicacanthus cusia. As for Dyers Woad, until the Ming Dynasty, the authentic product was Dyers Woad of the European Verbena Herb family, but starting from the Qing Dynasty, "Dyers Woad leaf" became a general name for Dyers Woad of the European Verbena Herb family and various blue leaves containing indigo. Recently, due to the emphasis on the pharmacological activity of indigo glycosides, Dyers Woad of the European Verbena Herb family has been phased out, and the leaf of Isatis indigotica of the Brassicaceae family has become the authentic product. From the perspective of authenticity, Isatis indigotica is cultivated in both the north and south without a clear trend of authenticity, while Baphicacanthus cusia has a long history of cultivation in Fujian, which should be the authentic production area of strobilanthes root.

bubble_chart Variety verification

Ancient plant dyes were mainly from Gardenia and madder, with Shiji·Huozhi Liezhuan mentioning "a thousand acres of Gardenia and madder", madder root dyeing red, Gardenia dyeing yellow, and blue mainly coming from the indigo contained in plants. The Book of Songs·Xiaoya·Cailu says "picking blue all morning, not filling a lapel", the "blue" picked is used as a pigment. "Qing" is also related to "blue", Xunzi·Quanxue says: "Qing is taken from blue but is bluer than blue." Shiji·Sanwang Shijia quotes a biography saying: "Qing is taken from blue but is bluer than blue." Shuowen says: "Blue, the grass that dyes green." Bencao Jing has "Lanshi", Bielu says: "Its stems and leaves can dye green." The character "Qing" has not been explained by various scholars, suspected to mean the later "indigo" character, Yupian says: "Indigo, dyed with blue", referring to the indigo dye used in later generations, which is refined and extracted from the plant "blue".

There are many plants containing indigo, and the "blue" referred to in different times and places in ancient times was not of a single kind. Based on the "Erya" which states "Zhen, Ma Lan" and Guo Pu's annotation "now known as Da Ye Dong Lan," and Xing Bing's note "now used for dye," it was thus believed that the blue fruit mentioned in the Bencao Jing was the fruit of Isatis indigotica from the Brassicaceae family. However, this assertion may be problematic. During the Eastern Han Dynasty, blue was extensively cultivated as an economic plant. The "Taiping Yulan" volume 996 quotes Xie Cheng's "Book of the Later Han": "Hongnong Yang Zhen, styled Boqi, often planted blue for his livelihood. His students, fearing Yang Zhen was getting old, offered to help with the labor, but Yang Zhen persuaded them to stop." It also quotes Zhao Qi's preface to "Ode to Blue": "While seeking medical treatment in Yanshi, I passed through Chenliu, where the local people all made a living by planting blue for dyeing. The fields of blue stretched as far as the eye could see, with no millet or sorghum planted. Moved by their neglect of fundamentals and focus on trivialities, I composed this ode." The fruit of this blue plant should be the blue fruit mentioned in the Bencao Jing. Additionally, according to the preface of "Qimin Yaoshu" quoting Eastern Han's Zhongchang Tong: "How is this different from insects in the smartweed, unaware of the sweetness of blue?" This proves that the "blue" of the Eastern Han was indeed Polygonum tinctorium from the Polygonaceae family, and not any other plant.

Polygonum tinctorium is mainly distributed in the northern regions, which aligns with records such as Hongnong Yang Zhen planting indigo, Zhao Qi passing through Chenliu and seeing vast fields of indigo, and the Bencao Jing stating "the indigo fruit grows in the plains of Henei." By the Northern and Southern Dynasties, the northern text "Qimin Yaoshu" had a dedicated section on indigo cultivation methods. According to Mr. Miao Qiyu's research, Jia Sixie's discussion of "indigo" also refers to Polygonum tinctorium. However, Tao Hong-jing, located in the south, had a different view on "indigo." The "Jizhu" states: "The pointed leaves are superior," and this "indigo" is as Su Jing mentioned, "as Tao cited, it is Isatis indigotica," originally a cruciferous plant, Isatis indigotica.

The "Xinxiu" mentions three types of indigo: "One type, about two inches in circumference and three to four fen thick, comes from Lingnan and is said to treat toxic swellings. The imperial court names this herb 'wood indigo seed.' As Tao cited, it is Isatis indigotica, whose leaves are pounded to make dye. According to the classics, the one used is the fruit of Polygonum tinctorium, whose seedlings resemble Polygonum but are not pungent. The juice of this herb treats heat toxin, unmatched by other indigos. Moreover, both types of indigo are now used for dyeing. Isatis indigotica is used for dyeing blue, while Polygonum tinctorium cannot be used for dyeing but only for making green." Su Jing's mentioned Polygonum tinctorium and Isatis indigotica have been previously discussed, while the wood indigo from Lingnan seems to be the leguminous plant Indigofera tinctoria L. Chen Cang-qi also agrees with Su, stating "Polygonum tinctorium is most suitable for medicinal use." The "Shu Bencao" illustrated classic describes the indigo fruit as Polygonum tinctorium: "Leaves resemble water Polygonum, flowers are red and white, seeds are like Polygonum seeds but larger and black, found in low wetlands, commonly cultivated."

It grows about two to three feet tall, leaves resemble water Polygonum, flowers are red and white, seeds are like Polygonum seeds but larger and black, harvested in May and June. There are several types of indigo: wood indigo from Lingnan, not used medicinally; Isatis indigotica, used for dyeing, also called horse indigo, as mentioned in the "Erya"; and Polygonum tinctorium, used only for dyeing green, not for making dye, which is the type used in medical prescriptions. Additionally, in Fuzhou, there is a type of horse indigo with leaves year-round, resembling bitter herb, locals harvest it with roots, bake, pound, sieve, and take with wine to treat women's blood disorders effectively. In Jiangning, there is a type called Wu indigo, growing in February and March, resembling Artemisia, with green leaves and white flowers, cold nature to remove heat and toxin, stopping hematemesis. These two types, though different, both bear the name indigo, and ancient prescriptions often used Wu indigo, possibly this type, hence appended here." Besides the three types mentioned in "Xinxiu," the Fuzhou horse indigo, combined with the "Zhenglei" medicinal illustrations, can be confirmed as Baphicacanthus cusia of the creeping rostellularia herb family (Figure 1), while Wu indigo remains unidentified.

Regarding Su Song and others' view that Polygonum tinctorium is the authentic product, Kou Zong-shi strongly disagrees. The "Bencao Yanyi" criticizes: "The indigo fruit is the fruit of the large indigo, calling it Polygonum tinctorium is incorrect, as the 'Erya' states. It is indispensable for detoxifying various drugs." Regarding the large indigo, the "Tongzhi" volume 75 states "large indigo resembles mustard," likely referring to the cruciferous Isatis indigotica. Influenced by the "Yanyi," the "Jiuhuang Bencao" also considers Isatis indigotica as the authentic product. The book's entry on large indigo states: "Now found everywhere, commonly cultivated in gardens. Seedlings over a foot tall, leaves resembling cabbage leaves but slightly thicker and narrower, pale pink-green, stems branching with yellow flowers, forming small pods with black seeds. Materia medica states Isatis indigotica can be used for dyeing blue, named for its leaves resembling cabbage, also called horse indigo." Based on this book's morphological description and medicinal illustrations, it can be confirmed as Isatis indigotica (Figure 2).

Until the Song Dynasty, the medicinal parts of "indigo" had always followed the views of the Bencao Jing, mainly using the fruit, occasionally using the stems and leaves, and prescriptions were mostly named "indigo fruit." Although the "Jizhu" and "Yanyi" mentioned the fruit of Isatis, the dominant species was still Polygonum tinctorium. However, from the Song Dynasty onwards, the situation changed somewhat. Song Dynasty medical prescriptions began to use the root of "indigo" as medicine, with prescriptions written as "indigowoad root," and even in some Song and Yuan medical prescriptions, it was directly referred to as "Isatis Root," such as in Volume 5 and Volume 10 of Xiao'er Weisheng Zongwei Lunfang, the "Baoding Collection" for treating pregnancy-related illnesses, Volume 10 of Sanyin Jiyi Bingzheng Fanglun's detoxification pill, and Yuan Dynasty works like "Yilei Yuanrong" and "Shiyi Dexiao Fang." The change in medicinal parts also led to differences in plant sources.

According to "Shiming·Shishuqi," it is said that "ban (板) means pan (昄)," which raises the suspicion that "Isatis Root" might be an abbreviation of "pan indigowoad root." In "Shi·Dayajuan A," it is written, "Your land and territory are vast and prosperous, and also very abundant," where "pan (昄)" means "large." Therefore, "panlan (昄藍)" means "large blue." Since "horse (馬)" also carries the meaning of "large," Li Shi-zhen believed that Isatis Root should be the root of "horse blue." The "Gangmu" states: "The leaves of horse blue are like those of bitter lettuce, which is what Guo Pu referred to as large-leaf winter blue, commonly known as banlan (板藍)." According to this view, the authentic product at that time should be the root of strobilanthes, specifically Baphicacanthus cusia from the creeping rostellularia herb family. On the other hand, as mentioned in "Bencao Tujing," "Isatis indigotica, which can be used to make dye, is also called horse blue." Additionally, both "Bencao Yanyi" and "Jiuhuang Bencao" regard Isatis indigotica as the authentic "blue." Therefore, the root of Isatis indigotica from the Brassicaceae family can also be used as Isatis Root. If this reasoning is correct, the medicinal use of Isatis Root and strobilanthes root began in the Song Dynasty. As for Polygonum tinctorium, which has long been used for its fruit as the authentic "blue fruit," its root is not the mainstream variety of "indigowoad root."

The term "Dyers Woad" first appeared in "Mingyi Bielu," where its stem is used medicinally. The text states: "Collect the stems in the third or fourth month and dry them in the shade." Tao's annotation adds: "This is often used in prescriptions for cold-damage disease. It is not mentioned in the 'Benjing,' but it is now found in the eastern regions and nearby areas, growing about a foot tall with purple stems." Based solely on the brief description in "Bielu's Collected Annotations," it is insufficient to determine the species of Dyers Woad. However, the entry on "blue fruit" in "Bielu" states that "its stems and leaves can be used to dye blue," and Tao mentions that "Benjing" does not include Dyers Woad, both of which indicate that "Dyers Woad" and "blue fruit" are not the same thing.

Starting in the Tang Dynasty, its leaves were also used. "Xinxiu" states: "Dyers Woad uses both leaves and stems, not just the stems." "Bencao Tujing" describes: "It grows in spring, with greenish-purple stems resembling the seedlings of Dianthus, red-purple flowers similar to Polygonum, and also resembling Lilac Daphne, with yellow roots." Based on this description, it seems to belong to the Polygonum tinctorium family. However, according to the medicinal illustrations of Dyers Woad from Xinzhou in "Zhenglei," especially the Dyers Woad illustration in "Lyuchanyan Bencao," it can be confirmed as Dyers Woad Clerodendrum cytophium Turcz. from the European Verbena Herb family. Notably, "Lyuchanyan Bencao" separately lists "qinglan (青藍)," with text derived from the "blue fruit" entry in "Zhenglei," but the illustration is of Baphicacanthus cusia from the creeping rostellularia herb family. This at least indicates two issues: first, the plant sources of "blue" and "qing" were different in the Song Dynasty; second, Baphicacanthus cusia being called "qinglan" laid the groundwork for later confusion between Dyers Woad leaves and Isatis Root in terms of species.

During the Ming and Qing Dynasties, Dyers Woad from the European Verbena Herb family was still regarded as the authentic product. "Gangmu" states: "Dyers Woad is found everywhere, growing two to three feet tall, with round stems, leaves three to four inches long, green on the surface and pale on the back, growing in pairs. It blooms in August with small red flowers in clusters, producing green fruits the size of pepper grains, which turn red in September." "Zhiwu Mingshi Tukao" also mentions: "The leaves are four to five inches long, with five-petaled round purple flowers. The fruits are green when unripe and turn black when mature. When the fruits are ripe, the petals remain, resembling a tray. Locals all recognize it. In summer, it is used to make drinks to quench thirst."

In theory, Clerodendrum cytophium from the European Verbena Herb family, as the authentic Dyers Woad, has no relation to "blue." This plant does not contain indigo and cannot be used to make dye. The reason it became confused with indigo-containing plants like Baphicacanthus cusia, Isatis indigotica, and Polygonum tinctorium is due to other reasons.

During the era of "Bencao Jing," the fruit of "blue" was used medicinally and was called "blue fruit." Later, stems and leaves were also used, with the prescription name "blue fruit leaves." For example, in "Zhouhou Fang," Volume 3, citing "Meishi Fang," it is used to treat abnormal rising of qi cough: "Soak blue fruit leaves in water for a long time, then mash and extract the juice, take one liter on an empty stomach." It is also simply called "blue leaves," as in "Qianjin Yaofang," Volume 18, for treating sores on the lips: "Extract the juice from ten pounds of blue leaves in August and wash the affected area." The name "blue leaves" is still mentioned in "Bencao Gangmu," "Shennong Bencao Jingshu," and "Materia Medica Chengyabanji," indicating that it was not confused with the leaves of Dyers Woad at the time.

The confusion between Dyers Woad and blue leaves began in the Qing Dynasty, when Benjing Fengyuan merged Bielu Dyers Woad and "Tujing" Xiaoqing into the blue fruit entry. Zhang Lu stated: "Benjing uses blue fruit, which is the seed of Dyers Woad, and this is the so-called Polygonum tinctorium." Further examination reveals that the use of Dyers Woad in Qing Dynasty medical prescriptions far exceeded that of blue leaves, which may indicate that Dyers Woad and blue leaves gradually merged into one, with "Dyers Woad leaves" becoming a general term that includes European Verbena Herb family Dyers Woad and various blue leaves containing indigo. Recent chemical and pharmacological research has confirmed the pharmacological activity of indigo glycosides, leading to the initial elimination of European Verbena Herb family Dyers Woad, which does not contain indigo glycosides. Subsequently, to adhere to the principle of one drug, one substance, based on the opinions of some material medica experts and combined with common usage practices, the leaves of Isatis tinctoria from the Brassicaceae family were established as the only authentic product of Dyers Woad leaves.

Indigo is recorded in the "Kaibao", originally imported from foreign countries. According to the "History of the Northern Dynasties", the state of Cao (present-day Afghanistan) was abundant in Indigo. The "Kaibao" states that it "comes from Persia". Indigo is an artificial product made from indigo-containing plants, specifically the blue foam that forms on the surface of the liquid during the indigo-making process. Since China was able to produce indigo early on, with methods detailed in the "Qimin Yaoshu", it is likely that by the Song Dynasty, China was able to produce Indigo on its own and did not need to rely on imports. The "Kaibao" mentions that Taiyuan, Luling, and Nankang all produced Indigo, and also states that "the purple-blue foam on the dye vat is used, with the same function as Indigo". According to this, the dried foam is Indigo, as seen in the "Tiangong Kaiwu".

bubble_chart Historical Evolution of Authentic Production Areas

"Blue" was widely cultivated as an economic crop in ancient times, and its varieties were also very diverse, so there was no so-called authentic production area. Today, the Isatis tinctoria used as the genuine product for Dyers Woad leaves and Isatis Root, with a clear correspondence between variety and production area, should be based on the "Da Lan" recorded in the "Jiuhuang Bencao". As for the "Yaowu Chuchan Bian" stating that "indigowoad root and Dyers Woad are best produced in Beiliu, Guangxi", because the variety is unclear, it cannot be determined. The earliest record of Ma Lan is the Fuzhou Ma Lan in the "Zhenglei". Fujian has been the authentic production area for today's "strobilanthes root" since the Song Dynasty, possibly because Ma Lan has a high indigo content, making the "Jian Indigo" produced from it the most famous. As for the literature records on the production areas of Dyers Woad, the plants referred to are mostly Dyers Woad of the European Verbena Herb family, which have now been phased out, so they should not be used as proof of authenticity.