Gui zhi is one of the first herbs that students encounter. On the surface, the differences between gui zhi (cinnamon twig) and rou gui (cinnamon bark) seem dramatic and distinct: gui zhi releases the exterior and is often used to reach the surface and extremities, while rou gui warms the interior and returns fire to its source. Yet if we look deeper, the historical situation regarding the plant parts used as gui zhi vs. rou gui is nuanced, and their identity has changed over time.
Materia medica scholars have devoted significant attention to this topic for centuries. In the modern era, gui zhi refers to the tender twigs of the cinnamon tree. However, ben cao literature suggests that gui zhi initially referred to the distal bark of the cinnamon tree rather than the tender twigs that are used today.
Accordingly, the Japanese Pharmacopoeia only includes the bark of cinnamon. All classical formulas currently prescribed in Japanese Kampo use cinnamon bark (桂皮) instead of cinnamon twig (桂枝). Similarly, some Chinese experts that focus on classical formulas (such as Prof. Huang Huang 黃煌 from Nanjing) use rou gui instead of gui zhi when prescribing formulas from the Shang Han Lun and the Jin Gui Yao Lue, aiming to more accurately reflect the material used in ancient times.
How did the material used as gui zhi change over time?
Early materia medica texts did not differentiate rou gui and gui zhi prior to the Song dynasty (960-1279 CE). While various specifications of cinnamon bark were described from the Han dynasty through the Song dynasty, there are no references to the tender twigs until the 12th century. Although the twigs gradually began to be used as a form of gui zhi from that point onward, even relatively late texts such as the Qing dynasty Essentials of the Materia Medica (Ben Cao Bei Yao, 1694 CE) described gui zhi as the tender bark of the branches (i.e., not the twigs that we use today).
Given that we translate “gui zhi tang” as “cinnamon twig decoction,” it seems counterintuitive to consider that Zhang Zhongjing probably never used the twigs. However, the zhi (枝) in gui zhi 桂枝 can be translated as either branch or twig, and historical changes in gui zhi have been extensively investigated by generations of scholars. For example, in 1116 CE, the Song dynasty medicinal identification expert Kou Zongshi succinctly stated in the Extension of the Materia Medica (Ben Cao Yan Yi): “[the material that Zhang] Zhongjing referred to as gui zhi is branch bark.”
What did Zhang Zhongjing use?
In the Shang Han Lun and Jin Gui Yao Lue, the only name that appears is gui zhi. The medicinal material was not differentiated between applications such as the exterior-resolving gui zhi tang vs. the warming and kidney-supplementing formula shen qi wan. While the text does not provide descriptive detail, it specifies that the outer bark should be removed (qu pi 去皮). Since the tender twigs have a very thin cortex with little flavor in the wood below, scholars argue that removal of the outer layer of bark only makes sense if the material used was the bark rather than the tender twigs.
The names gui zhi and rou gui were not used in the Shen Nong Ben Cao Jing (which slightly preceded the Shang Han Lun), but all the forms of cinnamon that it recorded utilized the bark, with no mention of the tender twigs. In fact, the names “gui zhi” and “rou gui” did not appear in ben cao literature until the Tang dynasty.
Initially, rou gui and gui zhi were regarded as synonyms. The Newly Revised Materia Medica (Xin Xiu Ben Cao) was published by the Tang dynasty government in 659 CE, and it stated that “rou gui is also called gui zhi” (肉桂一名桂枝). Similarly, in the Five Dynasties period, the Materia Medica of Shu [Sichuan] (蜀本草 Shu Ben Cao, 10th century) noted that “the tender branch bark of mu gui 牡桂 [an ancient term applied to cinnamon]… is called gui zhi; it is also called rou gui.” The names gui zhi and rou gui both referred to “tender branch bark with thick flesh that was curled into a half roll, with an acrid and beautiful aroma.”
In this era, thick old bark was regarded as inferior to tender branch bark. After removing the outer cortex (cork) from the branch bark, the material was regarded as gui xin (桂心 “cinnamon heart”), which was the highest quality form. During the Tang dynasty through the Five Dynasties period (roughly 7th to 10th century), the most prominent name used in literature was gui xin. In excavated manuscripts from Dunhuang that preceded the Song dynasty revisions of Zhang Zhongjing’s work, the ingredients for formulas like gui zhi tang and ge gen tang listed gui xin rather than gui zhi.
Makoto Mayanagi (真柳誠), a leading contemporary expert on ben cao literature, has researched this issue in great detail. He notes that the term gui xin (cinnamon heart) was frequently used in extant texts that preserved Zhang Zhongjing’s formulas prior to the Song dynasty revisions of the Shang Han Lun and Jin Gui Yao Lue. In an article titled “Lin Yi changed the names of cinnamon-related medicinals in Zhang Zhongjing’s texts to gui zhi”, Mayanagi presents extensive evidence to argue that Song dynasty revisions to Zhang Zhongjing’s work systematically harmonized the names to gui zhi, which at the time was largely synonymous with gui xin and rou gui.
Physical specimens provide additional material evidence that supports this perspective. Specimens found in the Mawangdui tombs from 168 BCE consist of cinnamon bark with the rough outer cortex removed. While textual records from Mawangdui contain many terms related to cinnamon, there is no mention of gui zhi. Additionally, specimens of cinnamon remain intact at the Shosoin Repository in Nara, Japan. Sent from Tang dynasty China to Japan as an Imperial gift in 756 CE, these specimens also consist of bark with the rough outer cortex removed, and written records of the collection do not mention gui zhi.
When did distinctions between gui zhi and rou gui emerge?
Song dynasty materia medica texts, such as Tang Shenwei’s Materia Medica Arranged According to Pattern (Zheng Lei Ben Cao) from the late 11th century, did not yet separate gui zhi and rou gui into individual monographs. However, Song dynasty authors preserved the knowledge from previous generations in comprehensive printed texts, and added important distinctions in the context of cinnamon.
The tender twigs were first recorded by Chen Cheng 陳承, who referred to them as liu gui 柳桂 (“willow cinnamon”). In his 11th century Additional Statements on the Materia Medica (Ben Cao Bie Shuo), he stated: “gui zhi refers to the branches, not the main trunk; it is light and floating, and can effuse and disperse. At present, there is also a variety known as liu gui, which consists of the tender twigs of cinnamon. It is particularly suitable for reaching the upper burner.”
Over time, the trunk bark and branch bark began to be used as rou gui instead of gui zhi, and the identity of gui zhi gradually expanded to include the twigs in addition to the tender branch bark. In his Shang Han Fa Wei Lun (Treatise on the Subtleties of Cold Damage, 1130 CE), Xu Shuwei (許叔微) stated the “gui zhi in [Zhang] Zhongjing’s gui zhi tang uses the thin, distal, light branches of cinnamon.”
During this era, gui zhi and rou gui began to be differentiated in their applications. For example, Xu Shuwei stated: “rou gui is thick and full, it is used to treat the five viscera via its heavy nature; gui zhi is light and is used to treat cold damage via its effusing and dispersing [nature].” This clinical distinction between gui zhi and rou gui has continued to the present day.
Further developments
The Compendium of Materia Medica (Ben Cao Gang Mu, 1596 CE) divides cinnamon into several different specifications. The author Li Shizhen summarized the conclusions of previous scholars and attempted to clarify the distinctions between terms such as gui zhi 桂枝, rou gui 肉桂, guan gui 官桂, gui xin 桂心, mu gui 牡桂, and jun gui 菌桂.
Li Shizhen incorporated rou gui and gui zhi into separate sections of a single cinnamon monograph. He regarded the single name gui 桂 from the Miscellaneous Records of Famous Physicians (Ming Yi Bie Lu, 490 CE) to refer primarily to rou gui, and noted that it is used after removing the rough outer cortex. He also stated that if the outer cortex and the inner cortex were removed, the material is described as gui xin. He noted that guan gui referred to high-quality cinnamon that was gifted to officials, and this interpretation has endured to the modern era.
The Ben Cao Gang Mu lists gui zhi under the heading of mu gui, stating that is “thin and bland, used after discarding the rough outer cortex. That which is thinnest is called gui zhi. The tender twigs are called liu gui.” Li Shizhen also quoted Li Gao (Li Dongyuan) as saying: “[cinnamon with] thin qi is gui zhi; [cinnamon with] thick qi is rou gui. Thin qi is floating and discharging, so gui zhi moves upward and resolves the exterior. Thick qi is effusing and hot, so rou gui moves downward to supplement the kidney.”
In 1624 CE, gui zhi appeared under its own unique heading in the Treasury of Words on the Materia Medica (Ben Cao Hui Yan). The text described gui zhi as branch bark, and appears to be the first instance of gui zhi having its own individual monograph in ben cao literature. Similarly, Essentials of the Materia Medica (Ben Cao Bei Yao, 1694 CE) also featured a distinct monograph for gui zhi and described it as branch bark.
By the 18th century, it appears that the tender twigs were already widely used as gui zhi. The text Encountering the Sources of Materia Medica (Ben Jing Feng Yuan, 1695 CE) states: “gui zhi refers to the branches from the highest point; it is also called liu gui (willow cinnamon). It is thus named because it is thin and tender like willow twigs.” This suggests that gui zhi was synonymous with liu gui at the time.
The Golden Mirror of Orthodox Medicine (Yi Zong Jin Jian) also implies that the tender twigs were a mainstream form of gui zhi by 1740 CE. It states: “In the formula gui zhi tang, the words ‘remove the cortex’ (去皮) are listed below gui zhi. All the acrid, sweet qi and flavor resides entirely in the cortex, if it is removed there is only dead wood. How can it resolve the flesh and promote sweating? Later editions should remove these two words.” This statement suggests that the tender twigs were the primary material used as gui zhi.
In 1769 CE, the text Seeking Accuracy in the Materia Medica (Ben Cao Qiu Zhen) described gui zhi as the shavings of branches from rou gui. However, the text Essential Differentiation of Medicinals (Yao Yao Fen Ji) from 1773 CE suggests that the tender twigs were already the primary product on the market. It states: “at present, all gui zhi is liu gui. Why is this? While gui zhi is more tender and light than the trunk bark used as rou gui, it is not only the thin twigs. At present, all the gui zhi in use consists of extremely thin twigs; it is liu gui. The ancients called gui zhi “thin cinnamon,” which is now used as a counterfeit form of rou gui. It can pass as rou gui because people believe that gui zhi refers to liu gui. People confuse the word “branch” and assume that liu gui is gui zhi; they do not know that although gui zhi is tender and light, it is not necessarily thin and small. They do not know that in addition to the name gui zhi, there is also the name liu gui. Thus, vendors mix them, while people remain oblivious.”
By the late Qing dynasty, rou gui was sourced from thick bark, including truck bark, which was originally considered less desirable than branch bark in early literature. The main market material for gui zhi had shifted from distal branch bark to the tender twigs that we use today.
Conclusion
A systematic literature review by Liu Canlan (刘灿坤), titled “Ben Cao Investigation into the Plant Parts Used Medicinally as Gui Zhi” was published in 1995. Liu summarizes three primary points: 1) Up through the Tang dynasty, rou gui and gui zhi both referred to the same medicinal substance, but their applications varied based on dosage. Formulas with smaller dosages tended to be used for dispersing and effusing, while larger doses were used to sink into the internal viscera. The plant part used medicinally was the bark, either from the branches or distal branches. 2) From the Song dynasty to the Qing dynasty (roughly 12th century to the early 20th century), rou gui referred to the trunk or branch bark. Gui zhi referred to the bark from the smaller distal branches; the most tender twigs were also known as liu gui. 3) In the modern era, gui zhi refers to the tender twigs, and the trunk and branch bark are known as rou gui.
Contemporary materia medica texts speculate that the changes in gui zhi over time may be related to more comprehensive utilization of natural resources, but this is not explicitly stated in historical sources. Scholars such as Tang Yixiao (汤一笑) point out that when the tender twigs appeared to become the mainstream form of gui zhi in the 1700s, trade from southern regions was disrupted by political instability. Scarcity of wild resources was reflected in the high fees charged for harvesting cinnamon in prized production regions during this era. This may have encouraged the use of the tender twigs, which can be harvested without damaging the tree.
Over the centuries, many herbs have evolved due to changes in natural resources, processing, and advances in cultivation. For example, other common herbs were similarly not yet differentiated into their present market forms in early works such as the Shang Han Lun, including peony (bai shao/chi shao) and atractylodes (bai zhu/cang zhu). As with cinnamon, our modern concept of these medicinals has evolved over time based on historical changes in the available market materials and theory surrounding their use.
When we study Chinese herbs, our concept of their actions is influenced by the way that they were applied in classical formulas. We learn that gui zhi and bai shao harmonize ying and wei, a concept rooted in the Shang Han Lun. Similarly, we learn that gui zhi unblocks the bladder’s qi transformation function to treat swelling; this is exemplified in the formula Wu Ling San, where it is combined with bai zhu. However, during Zhang Zhongjing’s time, neither cinnamon, atractylodes, nor peony were differentiated into the forms that we use today. These distinctions were introduced by the editors in the Song dynasty that published the versions of the Shang Han Lun and Jin Gui that we use today. In fact, the official botanical sources of cinnamon, peony, and atractylodes are still interpreted differently in China, Japan, and Korea today.
Data on the most commonly prescribed Chinese herbs from Taiwan’s National Health Insurance shows that gui zhi ranks 20th while rou gui ranks 45th. At Legendary Herbs, gui zhi ranks in the top ten. We recently ran out of gui zhi for the first time since we started Legendary Herbs in 2006; to my surprise, few people used rou gui as a substitute. Fortunately, we have gui zhi back in stock now!
Guizhi in the Bencao Pinhui Jingyao (Photo credit: Eric Brand, copyright reserved)
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