Camellia sinensis explained

Camellia sinensis is a species of evergreen shrub or small tree in the flowering plant family Theaceae. Its leaves, leaf buds, and stems can be used to produce tea. Common names include tea plant, tea shrub, and tea tree (unrelated to Melaleuca alternifolia, the source of tea tree oil, or the genus Leptospermum commonly called tea tree).

White tea, yellow tea, green tea, oolong, dark tea (which includes pu-erh tea) and black tea are all harvested from one of two major varieties grown today, C. sinensis var. sinensis and C. s. var. assamica,[1] but are processed differently to attain varying levels of oxidation with black tea being the most oxidized and white being the least.[2] Kukicha (twig tea) is also harvested from C. sinensis, but uses twigs and stems rather than leaves.

Description

Camellia sinensis is native to East Asia, the Indian Subcontinent, and Southeast Asia, but it is today cultivated all around the world in tropical and subtropical regions. It is an evergreen shrub or small tree that is usually trimmed to below 2m (07feet) when cultivated for its leaves. It has a strong taproot. The flowers are yellow-white, 2.5– in diameter, with seven or eight petals.

The seeds of C. sinensis and C. oleifera can be pressed to yield tea oil, a sweetish seasoning and cooking oil that should not be confused with tea tree oil, an essential oil that is used for medical and cosmetic purposes, and originates from the leaves of a different plant.

The leaves are 4– long and 2– broad. Fresh leaves contain about 4% caffeine, as well as related compounds including theobromine.[3] The young, light-green leaves are preferably harvested for tea production when they have short, white hairs on the underside. Older leaves are deeper green. Different leaf ages produce differing tea qualities, since their chemical compositions are different. Usually, the tip (bud) and the first two to three leaves are harvested for processing. This hand picking is repeated every one to two weeks.

In 2017, Chinese scientists sequenced the genome of C. s. var. assamica.[4] It contains about three billion base pairs, which was larger than most plants previously sequenced.[5]

Taxonomy

The generic name Camellia is taken from the Latinized name of Rev. Georg Kamel,[6] SJ (1661–1706), a Moravian-born Jesuit lay brother, pharmacist, and missionary to the Philippines.

Carl Linnaeus chose his name in 1753 for the genus to honor Kamel's contributions to botany[7] (although Kamel did not discover or name this plant, or any Camellia,[8] and Linnaeus did not consider this plant a Camellia but a Thea).

Robert Sweet shifted all formerly Thea species to the genus Camellia in 1818.[9] The name sinensis means "from China" in Latin.

Four varieties of C. sinensis are recognized.[10] Of these, C. sinensis var. sinensis and C. s. var. assamica (JW Masters) Kitamura are most commonly used for tea, and C. s. var. pubilimba Hung T. Chang and C. s. var. dehungensis (Hung T. Chang & BH Chen) TL Ming are sometimes used locally. The Cambodia type tea (C. assamica subsp. lasiocaly) was originally considered a type of assam tea. However, later genetic work showed that it is a hybrid between Chinese small leaf tea and assam type tea.[11]

Tea plants are native to East Asia, and probably originated in the borderlands of north Burma and southwestern China.[12]

Chinese (small leaf) tea may have originated in southern China possibly with hybridization of unknown wild tea relatives. However, since no wild populations of this tea are known, the precise location of its origin is speculative.

Given their genetic differences forming distinct clades, Chinese Assam type tea (C. s. var. assamica) may have two different parentages – one being found in southern Yunnan (Xishuangbanna, Pu'er City) and the other in western Yunnan (Lincang, Baoshan). Many types of Southern Yunnan Assam tea have been hybridized with the closely related species Camellia taliensis. Unlike Southern Yunnan Assam tea, Western Yunnan Assam tea shares many genetic similarities with Indian Assam type tea (also C. s. var. assamica). Thus, Western Yunnan Assam tea and Indian Assam tea both may have originated from the same parent plant in the area where southwestern China, Indo-Burma, and Tibet meet. However, as the Indian Assam tea shares no haplotypes with Western Yunnan Assam tea, Indian Assam tea is likely to have originated from an independent domestication. Some Indian Assam tea appears to have hybridized with the species Camellia pubicosta.[13] [14]

Assuming a generation of 12 years, Chinese small leaf tea is estimated to have diverged from Assam tea around 22,000 years ago; this divergence would correspond to the last glacial maximum,[13] [14] while Chinese Assam tea and Indian Assam tea diverged 2,800 years ago.

Chinese small leaf type tea was introduced into India in 1836 by the British and some Indian Assam type tea (e.g. Darjeeling tea) appear to be genetic hybrids of Chinese small leaf type tea, native Indian Assam, and possibly also closely related wild tea species.[15]

Cultivars

Hundreds,[16] if not thousands of cultivars of C. sinensis are known. Some Japanese cultivars include:

Cultivation

Camellia sinensis is mainly cultivated in tropical and subtropical climates, in areas with at least 127 cm (50 in) of rainfall a year. Tea plants prefer a rich and moist growing location in full to part sun, and can be grown in hardiness zones 7–9. However, the clonal one is commercially cultivated from the equator to as far north as Cornwall and Scotland on the UK mainland.[19] [20] Many high quality teas are grown at high elevations, up to 2200m (7,200feet), as the plants grow more slowly and acquire more flavor.

Tea plants will grow into a tree if left undisturbed, but cultivated plants are pruned to waist height for ease of plucking. Two principal varieties are used, the small-leaved Chinese variety plant (C. s. sinensis) and the large-leaved Assamese plant (C. s. assamica), used mainly for black tea.

Chinese teas

The Chinese plant is a small-leafed bush with multiple stems that reaches a height of some 3m (10feet). It is native to southeast China. The first tea plant variety to be discovered, recorded, and used to produce tea dates back 3,000 years ago; it yields some of the most popular teas.

C. s. var. waldenae was considered a different species, C. waldenae by SY Hu, but it was later identified as a variety of C. sinensis.[21] This variety is commonly called Waldenae Camellia. It is seen on Sunset Peak and Tai Mo Shan in Hong Kong. It is also distributed in the Guangxi province.

Indian teas

Three main kinds of tea are produced in India:

Pests and diseases

See main article: List of tea diseases. Tea leaves are eaten by some herbivores, such as the caterpillars of the willow beauty (Peribatodes rhomboidaria), a geometer moth.

Health effects

See main article: Health effects of tea. Although health benefits have been assumed throughout the history of using tea as a common beverage, no high-quality evidence shows that tea confers significant benefits.[22] [23] In clinical research over the early 21st century, tea has been studied extensively for its potential to lower the risk of human diseases, but none of this research is conclusive as of 2017.[22]

Biosynthesis of caffeine

Caffeine, a molecule produced in C. sinensis, functions as a secondary metabolite and acts as a natural pesticide: it can paralyze and kill herbivorous insects feeding on the plant.[24] Caffeine is a purine alkaloid and its biosynthesis occurs in young tea leaves and is regulated by several enzymes.[25] [26] The biosynthetic pathway in C. sinensis is similar to other caffeine-producing plants such as coffee or guayusa.[27] Analysis of the pathway was carried out by harvesting young leaves and using reverse transcription PCR to analyze the genes encoding the major enzymes involved in synthesizing caffeine. The gene TCS1 encodes caffeine synthase. Younger leaves feature high concentrations of TCS1 transcripts, allowing more caffeine to be synthesized during this time. Dephosphorylation of xanthosine-5'-monophosphate into xanthosine is the committed step for the xanthosines entering the beginning of the most common pathway. A sequence of reactions turns xanthosine (9β--ribofuranosylxanthine) into 7-methylxanthosine, then 7-methylxanthine, then theobromine (3,7-dimethylxanthine), and finally into caffeine (1,3,7-trimethylxanthine).

See also

External links

Notes and References

  1. https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=506801 ITIS Standard Report Page Camellia Sinensis
  2. Book: Preedy, V.R. . Tea in Health and Disease Prevention . Elsevier Science . 2013 . 978-0-12-384937-3 . February 24, 2022 . 199–200 . 10 November 2023 . https://web.archive.org/web/20231110002808/https://books.google.com/books?id=k3HK2WuZrsYC . live .
  3. Web site: Purdue. Camellia sinensis. 18 February 2008. 24 September 2010. https://web.archive.org/web/20100924055240/http://www.hort.purdue.edu/newcrop/duke_energy/Camellia_sinensis.html. live.
  4. Xia EH, Zhang HB, Sheng J, Li K, Zhang QJ, Kim C, Zhang Y, Liu Y, Zhu T, Li W, Huang H, Tong Y, Nan H, Shi C, Shi C, Jiang JJ, Mao SY, Jiao JY, Zhang D, Zhao Y, Zhao YJ, Zhang LP, Liu YL, Liu BY, Yu Y, Shao SF, Ni DJ, Eichler EE, Gao LZ . 6 . The Tea Tree Genome Provides Insights into Tea Flavor and Independent Evolution of Caffeine Biosynthesis . Molecular Plant . 10 . 6 . 866–877 . June 2017 . 28473262 . 10.1016/j.molp.2017.04.002 . free .
  5. News: Secrets of tea plant revealed by science. Briggs. Helen. 2017-05-02. BBC News. 2017-05-02. en-GB. 6 August 2018. https://web.archive.org/web/20180806051540/https://www.bbc.co.uk/news/science-environment-39747720. live.
  6. Book: Stafleu FA, Cowan RS . 1976–1988 . Taxonomic literature: A selective guide to botanical publications and collections with dates, commentaries and types . 2nd . Bohn, Scheltema and Holkema . Utrecht. 978-9031302246 .
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  10. Book: Tianlu . Min . Bruce . Bartholomew . vanc . http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=200014043 . Flora of China . 18. Theaceae . 12 . 16 October 2011 . 29 December 2022 . https://web.archive.org/web/20221229180605/http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=200014043 . live .
  11. Wambulwa, MC, MK Meegahakumbura, R Chalo, et al. 2016. Nuclear microsatellites reveal the genetic architecture and breeding history of tea germplasm of East Africa. Tree Genetics & Genomes, 12.
  12. Book: Yamamoto . T . Kim . M . Juneja . L R . 1997 . 978-0-8493-4006-2 . Chemistry and Applications of Green Tea . CRC Press . 4 . For a long time, botanists have asserted the dualism of tea origin from their observations that there exist distinct differences in the morphological characteristics between Assamese varieties and Chinese varieties... Hashimoto and Shimura reported that the differences in the morphological characteristics in tea plants are not necessarily the evidence of the dualism hypothesis from the researches using the statistical cluster analysis method. In recent investigations, it has also been made clear that both varieties have the same chromosome number (n=15) and can be easily hybridised with each other. In addition, various types of intermediate hybrids or spontaneous polyploids of tea plants have been found in a wide area extending over the regions mentioned above. These facts may prove that the place of origin of Camellia sinensis is in the area including the northern part of the Burma, Yunnan, and Sichuan districts of China..
  13. Meegahakumbura . MK . Wambulwa . MC . Thapa . KK . etal . 2016 . Indications for three independent domestication events for the tea plant (Camellia sinensis (L.) O. Kuntze) and new insights into the origin of tea germplasm in China and India revealed by nuclear microsatellites . PLOS ONE . 11 . 5. e0155369 . 27218820 . 4878758 . 10.1371/journal.pone.0155369 . 2016PLoSO..1155369M . free .
  14. Meegahakumbura MK, Wambulwa MC, Li MM, Thapa KK, Sun YS, Möller M, Xu JC, Yang JB, Liu J, Liu BY, Li DZ, Gao LM . 3 . 2018. Domestication origin and breeding history of the tea plant (Camellia sinensis) in China and India based on nuclear microsatellites and cpDNA sequence data. Frontiers in Plant Science . 8. 2270 . 29422908 . 5788969 . 10.3389/fpls.2017.02270. free .
  15. Wambulwa . M. C. . Meegahakumbura . M. K. . Chalo . R. . Kamunya . S. . Muchugi . A. . Xu . J. C. . Liu . J. . Li . D. Z. . Gao . L. M. . Nuclear microsatellites reveal the genetic architecture and breeding history of tea germplasm of East Africa . Tree Genetics & Genomes . 2016 . 12 . 1 . 11 . 10.1007/s11295-015-0963-x. 15909964 .
  16. News: Tea Cultivar Database – World of Tea. World of Tea. 2017-05-09. en-US. 6 June 2017. https://web.archive.org/web/20170606164633/https://worldoftea.org/cultivar-database/. live.
  17. Web site: Identification of Japanese tea (Camellia sinensis) cultivars using SSR marker . . 1 November 2018 . 1 November 2018 . https://web.archive.org/web/20181101135900/http://agris.fao.org/agris-search/search.do?recordID=JP2008002305 . live .
  18. Web site: Varietal differences in the adaptability of tea [Camellia sinensis] cultivars to light nitrogen application ]. . 1 November 2018 . 1 November 2018 . https://web.archive.org/web/20181101135956/http://agris.fao.org/agris-search/search.do?recordID=JP2008003777 . live .
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  21. Ming TL . 1992 . A revision of Camellia sect. Thea . Acta Botanica Yunnanica . 14 . 2 . 115–132 . Chinese. .
  22. Web site: Black tea. MedlinePlus, US National Library of Medicine. 30 November 2017. 27 February 2018. 5 July 2016. https://web.archive.org/web/20160705113528/https://www.nlm.nih.gov/medlineplus/druginfo/natural/997.html. live.
  23. Web site: Green tea. National Center for Complementary and Integrative Health, US National Institutes of Health. 27 February 2018. 30 November 2016. 20 March 2015. https://web.archive.org/web/20150320021603/https://nccih.nih.gov/health/greentea. live.
  24. Nathanson JA . 42711016 . Caffeine and related methylxanthines: possible naturally occurring pesticides . Science . 226 . 4671 . 184–187 . October 1984 . 6207592 . 10.1126/science.6207592 . 1984Sci...226..184N .
  25. Li Y, Ogita S, Keya CA, Ashihara H . Expression of caffeine biosynthesis genes in tea (Camellia sinensis) . Zeitschrift für Naturforschung C . 63 . 3–4 . 267–270 . March 2008 . 18533472 . 10.1515/znc-2008-3-417. free .
  26. Kato M, Mizuno K, Fujimura T, Iwama M, Irie M, Crozier A, Ashihara H . Purification and characterization of caffeine synthase from tea leaves . Plant Physiology . 120 . 2 . 579–586 . June 1999 . 10364410 . 59297 . 10.1104/pp.120.2.579.
  27. Lin . Zhipeng . Wei . Jian . Hu . Yongqiang . Pi . Dujuan . Jiang . Mingguo . Lang . Tao . January 2023 . Caffeine Synthesis and Its Mechanism and Application by Microbial Degradation, A Review . Foods . en . 12 . 14 . 2721 . 10.3390/foods12142721 . 37509813 . 10380055 . 2304-8158 . free .