I have hesitated to post another research-based blog because I was skeptical that anyone would be interested in reading science writing on this kind of platform. Ultimately, however, I believe that a) there are many people like myself who want to take a deep-dive on topics pertinent to our food systems and b) there is no downside!
This research was reviewed and approved for accuracy and coverage by the instructors of Dr. Paul Gept’s fantastic crop evolution class back in 2018. I have re-structured the formatting and language to be a little more blog-friendly.
I learned so much writing this work and gained an even greater appreciation for the myriad of teas I have enjoyed…I hope you do too!

What is tea, really?

Camellia sinensis is a small evergreen tree with a strong taproot root system and alternate, lanceolate to obovate leaves. It favors warm temperatures varying between 14 and 27 degrees Celsius and a wet to dry climate with 121 centimeters or more of rain annually (Duke 1983). The large-leaf plant is found more in tropical regions and the small-leaf plant is found in temperate regions (Hasimoto 1971). Tea is propagated from seed or vegetatively and requires four to twelve years to bear seed. Most often the tea trees are planted in rows and are top-pruned to facilitate mechanical harvesting. Harvest typically takes place in the summer when the solar heat is the most intense and the bushes are plucked every 7-15 days (Duke 1983). Much of the harvested weight will be lost in the drying process and the leaves do not weigh much to begin with, so a skilled picker can only gather a little over a pound in a day of work (Du Feibao n.d). Currently, there are 61 countries around the world with at least one productive tea plantation. China is the largest producer in the world and has the greatest diversity of tea and tea styles. In second place is India, third is Kenya, fourth is Sri Lanka, and fifth is Turkey (Gebely 2017). Different varieties of tea arise primarily from various modes of processing the leaf. In China there are five categories of tea: green, black, wulong, compressed, and scented. Green tea is processed without fermentation, black tea is fermented before baking, and wulong is a partially fermented before baking. Compressed tea is a kind of tea which is compressed into bricks and is sold as a cheap alternative to black or green teas. Finally, scented tea is tea which has been infused with plants like jasmine, magnolia, and a growing number of flavors (Du Feibao n.d.). Green tea is pan-fired or steamed immediately after harvest to destroy the enzymes that would perform fermentation, they are then rolled on heated trays, and fired in dryers for the final drying stage. Black tea is first withered and dried to a fraction of their original moisture content, then they are rolled and spread out in a cool, humid room to ferment for one to five hours then fired and dried to cease the fermentation process. The final product has anywhere from 10-50 mg of caffeine per six ounces, which is a tenth to half of boiled coffee caffeine content. Black tea has far more caffeine than green tea thanks to fermentation. Tea has purported medicinal benefits, namely that it contains polyphenols (20-30%). Polyphenols are antioxidants, touted as good for the treatment of inflammation and disease prevention (Duke 1983). Tea drinking in China is a part of daily life and tea-houses are abundant in South China, where it has long been regarded as an important part of a healthy diet and life (Du Feibao n.d.).

Plant Sleuthing

Historical, linguistic, archaeological, botanical, and genetic evidence are compiled and discussed to hone in on the center of origin and centers of domestication for Camellia sinensis. The evidence is presented roughly in the order of the determined region size, from largest to smallest regions, and the significance of the findings, from the least to most heavily weighted. All brands of evidence are necessary to make an assessment.

An Emperor Rests under a tree

The oldest historical records of Camellia sinensis point to its origin in China. According to Chinese legend, it was Emperor Shennong, the Divine Farmer, who discovered tea. He was perched under a C. sinensis tree when a leaf fell into his boiling water. He found the infusion to be very refreshing and fragrant, and the tea has been popular ever since (The History of Tea n.d.). This was said to have occurred in the year 2737 BC. In 350 AD, scholar Kou P’o recorded the first strictly factual account of the use and horticulture of tea (Balentine 1992). In the sixth and 7th centuries, tea was used for medicinal qualities and by the seventh to 10th centuries, it became an art form common to all social classes (The History of Tea n.d.). Tea was introduced to Japan in 600 AD, Europe in 1610, and the American colonies in 1650 (Balentine 1992). Interestingly enough, it was not until the late 17th century that a European had even seen a tea plant. Dr. Wilhelm ten Rhyne lived in a trading post in Deshima off the coast of Nagasaki where he wrote his text on tea. In the early 19th century, English colonizers wanted to begin growing tea in India and they discovered wild tea trees growing in the hills of Assam. In 1905, the International Code of Botanical Nomenclature determined that the wild trees in Assam were Camellia sinensis and that it was native to the monsoon region of southeast Asia. This area includes Thailand, Burma, southwest China, and Assam (History of Tea: England n.d.).

“Cha” and “Te”

The linguistic history of Camellia sinensis supports the case for the origin of tea in China. Most names for Camellia sinensis come from either the Sinitic “cha” or the Min Nam Chinese “te”. In a collection of 230 words, 109 were derived from “cha” and 84 were derived from “te” (Östen 2013). The study finds that in the cases where tea grows naturally, such as in Burma, the words were not derived from these “cha” or “te” (Sonnad 2018). One could infer that in all other cases, tea could simply be a word used to describe other drinks where plants are steeped in hot water. For example, we call chamomile infused water chamomile tea even though it does not bare any relation to Camellia sinensis.

Interestingly enough, the words derived from the Sinitic “cha” followed trade routes on land and languages along the paths through Asia to East Africa, Central Europe, and North toward Russia. Meanwhile, the words derived from the Min Nam Chinese “te” followed sea routes through Southeast Asia, the Southern-most region of India, Southern and Western Africa, and Western and Southern Europe.

Digging for Tea Leaves

The unearthed tea in ancient sites around China provide the oldest archaeological record for Camellia sinensis. The following sites will be discussed: the Tianmu Mountain site in Ningbo, Zhejiang province, the Han Yangling Mausoleum in Chang’an, and the Gurgyam Cemetery in Ngari.

In 2001, the Tianmu Mountain site was discovered. This site has provided one of the earliest recordings of China’s Neolithic Age, with evidence for primitive activities ranging between 7,000 to 5,000 BC. In 2004, the roots of a tree were uncovered and two years later, tests showed that the roots contained theanine (Tea Cultivation 2015). Although present in various other plant and fungal species, it is present in far more substantial quantities in the Camellia Sinensis plant and has been used as a marker since this discovery in the early 1950s (Sakato 1949). In 2015, after almost a decade of testing, the Zhejiang Cultural Relics and Archaeological Research Center revealed that the tree roots belonged to Camellia sinensis, and that they were about 6,000 years old (Tea Cultivation 2015). While it is difficult to determine whether these trees were domesticated or cultivated for brewing tea in their time, there are clues at the site that have lead researchers to make educated inferences about the relationship between the ancient civilization and the trees. Researchers found traces of manual digging around the roots, pottery pieces around the roots, and a pottery utensil with a spout and a handle. Further research might be able to prove their theory that the cultivation and consumption of tea began 6,000 years ago.

The Han Yangling Mausoleum is located in Chang’an and was built for the Jing Emperor Liu Qi in 188-141 BC. Between 1998 and 2005, 86 outer burial pits were excavated by the Shaanxi Provincial Institute of Archaeology; pit DK15 contained partially decomposed plant remains. Several of the plants were identified, but there was one dark brown brick, dated between 255-80 BC that had no identifiable morphological features. Biomarker, calcium phytolith, and theanine and caffeine identification techniques revealed that the brick was in fact Camellia sinensis. This discovery showed that tea was grown 2100 years ago for human consumption. This is the oldest definitive record researchers have for tea cultivation and consumption.

The Gurgyam Cemetery site in the Ngari district of Tibet contained ceramic vessels, one of which was holding plant remains. The plant remains were studied in the same manner as at the Han Yangling Mausoleum and were determined to be Camellia sinensis of about the same age, 1800 years old. The researchers determined that these were not original sites of tea cultivation but were carried to these regions from Southwestern Yunnan China and adjacent regions (Lu et al. 2016).

A Family Tree

The botanical evidence for the origin of Camellia sinensis in China is ample, but the specific region of origin is contested. The tea plant is classified morphologically into two major categories: the temperate small-leaf and the tropical large-leaf. There are of course intermediate types and various tea leaves are produced in the plethora of environmental conditions to be found in China. This morphological classification gave rise to a theory of two places of origin. The specific regions of origin are thought to be between Yunnan and Assam in India for the Assam type and Southeastern China for the small-leafed type. According to Minoru Hasimoto in The Origin of the Tea Plant, this two-origin theory is lacking. Both Chinese and Assam varieties have the same chromosome number (2n=30) (Simura 1935) and there is a continuous variation from Southeastern China to India with a proposed origin in Sichuan, Yunnan, and Guizhou. In addition to these findings, wild gigantic tea trees have been found primarily in the Yunnan province and the border between Burma and Laos, but also in a few locations in Sichuan and Guizhou. These gigantic tea trees in some cases date back to over 1700 years old, stand taller than 14 meters high, and have branches 10 m long. These ancient, giant tea trees are thought to be relic species of the cultivated species. This article concludes that there is only one origin in the southwestern district of Sichuan/Yunnan (Hasimoto 1971). In 1950 in Nature, London, the center of origin of tea was determined to be in Central Asia, a relatively broad region of determination. The author identified secondary centers of dispersal in the Northwestern region of China and in the Irrawaddy region of Burma (Kingdon-Ward 1950). This study is consistent with the idea that there is one center of origin, even if it suggests independent secondary origins of domestication.

The Legend of DNA

The genetic evidence for the origin(s) of Camellia sinensis all point to southwestern China as the region of origin and is largely consistent with the botanical evidence. In Genetic diversity and relationship of clonal tea (Camellia sinensis) cultivars in China as revealed by SSR markers, researchers extracted genomic DNA from the young shoots of 185 clonal cultivars from 10 geographical regions of China and analyzed them at 58 SSR. Over 263 alleles and 605 genotypes were detected, and a high level of genetic diversity was determined. When diversity of tea cultivars from the different geographical regions of China was considered, diversity was, from highest to lowest, as follows: Guangdong, Sichuan/Chongqing, Fujian, Zhejiang, Yunnan, Anhui, Hunan, Guizhou, Hubei, Taiwan. Their genetic structure assays also suggested that Yunnan and Sichuan are the centers of origin for Camellia sinensis and concluded that China was the first place of tea cultivation (Fang et al. 2012).

The areas adjacent to Guangxi, Yunnan, and Guizhou are secondary centers of origin based on their geographic distribution of wild tea plants (Yao et al. 2005). A treasure reservoir of genetic resource of tea plant in Dayao Mountain investigated wild tea plants in the Dayao Mountain (Guangxi) and compared them to cultivars grown in other Chinese provinces such as Yunnan and Hunan. This study focused on the Guangxi region because research had been focused on wild teas growing in Yunnan and Guizhou provinces, despite the plentiful wild resources in Guangxi. The study found the teas of the Liuxiang population in the Dayao Mountain region to be the most primitive because they were the most widely distributed, had the greatest variation, and the richest diversity (Jiang 2018). This is not to say that the Liuxiang region represents the center of origin, but that it should be studied further in the future.

In the study Domestication Origin and Breeding History of the Tea Plant (Camellia sinensis) in China and India Based on Nuclear Microsatellites and cpDNA Sequence Data, researchers confirmed the existence of independent domestication sites for Chinese Assam in Southern Yunnan and Western Yunnan, Indian Assam in Assam of India, and Chinese type tea in Southern China. Additionally, the results indicated that the Chinese Assam type of Western Yunnan and the Indian Assam type in India arose from a single population in Southwest China/Indo-Burma/Tibet (Meegahakumbura et al. 2017). In short, the Indian Assam tea was likely introduced from China (Meegahakumbura 2016). From there, independent domestications occurred in Western Yunnan and Assam of India. The China type tea on the other hand has an entirely distinct genetic lineage and the specific origin remains unknown. Future studies should include broader sampling of wild tea plants in Southern China to determine the exact origin of domestication of tea in China (Meegahakumbura et al. 2017).

Wild Tree to lucrative Crop

Tea cultivars have been selected for morphological traits in China since as early as the eight century. In Domestication Origin and Breeding History of the Tea Plant (Camellia sinensis) in China and India Based on Nuclear Microsatellites and cpDNA Sequence Data almost a third of the tea samples were hybrids between tea types or between tea types and their wild relative C. taliensis (Meegahakumbura et al. 2018). From this we know that there has been hybridization of wild tea ancestors and domestication. In the study Genetic Divergence between Camellia sinensis and Its Wild Relatives Revealed via Genome-Wide SNPs from RAD Sequencing, they found that there were genic SNPs related to functional genes, most especially those involved in the secondary metabolic processes (Yang et al. 2016). This serves as genetic evidence for the domestication syndrome because secondary metabolism is selected on in domestication, among other traits. More revealing information about the key characteristics of the domestication syndrome, such as loss of seed shattering/pod dehiscence/fruit shedding and dormancy, are not so well understood for C. sinensis. Their seeds may or may not exhibit dormancy and evidence for loss of or reduced seed dispersal could not be found (Song et al. 2016).

Follow the Silk Road:
Southern China West

All evidence points to China as the center of origin of Camellia sinensis. Furthermore, the botanical and genetic evidence finds various locations in the southwestern region of China to be the site(s) of domestication. Using all the evidence found and discussed, tea likely originated in the southern region of China and domestication spread westward. In the southern Yunnan region, the Chinese Assam type was likely domesticated and resulted in two secondary domestications in Western Yunnan and the Assam of India. In the map below, the relevant sites are listed with bold-faced dots and the relevant provinces are labeled. The archaeological sites at Tianmu Mountain, the Han Yangling Mausoleum, and Guryam Cemetery discussed in this research create an interesting time-space gradient that is perhaps consistent with the proposed westward domestication of C. sinensis.

How could we be more sure?

To make a precise determination of the center of origin in the southern region of China, future studies should include wider sampling of wild tea plants, most especially in the provinces of Guizhou and Guangxi, which have been studied less extensively than Hunan, Sichuan, and Yunnan (Meegahakumbura et al. 2017, Jiang et al. 2018). Ancient tea gardens in Yunnan and elsewhere should be maintained and the local knowledge and experience should be documented and encouraged to preserve and conserve them in the future. These tea gardens are rich in species and diversity and are valuable genetic resources for future research (Qi et al. 2005).

More than just “hot leaf water”

…as my funny roommate so endearingly calls it. There is so much history, beauty, and work (past and present) that goes into that delightful cup. Nearly every plant we enjoy has undergone a similar journey, and for that, we should be very grateful!

Annalise

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Where Does Tea Come From? It's Not What You Think