Family, Genus and Species Limits

Borne in the leaf axil, a beautiful showy flower of Camellia sinensis.

Commonly known in the West as ‘Tea’, Camellia sinensis (L) O. Kuntze is an evergreen shrub assigned to the family Theaceae. The most recent circumscription of this family includes 3 sub-families: Theeae, Gordonieae and Stewartieae, which contain a total of 9 genera and circa. 195 species (Stevens, 2001-onwards). Some of the diagnostic features of the family include large and showy flowers which are actinomorphic, solitary and born in the axils of the leaves; leaves which are alternate and spirally or distichously arranged; and, simple leaves with toothed margins and no stipules (Heywood et al. 2007).

The fruit of Camellia spp is a 3-loculicidal capsule containing 3 distinctive rounded-cuneate seeds.

Camellia is the type genus for Theaceae, and can include as little as 119 species or as many as 280, depending on the species concept applied during delimitation (Vijayan et al. 2009). A key, morphological diagnostic feature of Camellia is the presence of a rounded or rounded-cuneate seeds with thick cotyledons (Vijayan et al. 2009). Carl von Linne originally placed Camellia sinensis in a genus known as Thea, and for many years Camellia and Thea were considered different genera. However, morphological, anatomical and biochemical studies have since proved that there is no realistic basis for differentiation. The generic boundaries have been redrawn so that Thea has now become part of Camellia (Wilson & Clifford, 1992).

Here are some morphological obervations of the Camellia sinensis plant we have growing in the tropical greenhouse.

The Camellia sinensis flowers in the tropical greenhouse have numerous stamens (>200) – a diagnostic feature of Camellias. Image attributed to Chris Reilly.

The plant in our greenhouse has flowers which have approximately 7-8 petals, and occur in clusters of 2-3 within the leaf axils.

This image shows the plant in the tropical greenhouse to have a range of axillary leaf angles. Image attributed to Chris Reilly.

An axillary leaf angle of less than 50 degrees is one of the diagnostic features of the China Tea Plant variety: Camellia sinensis var. sinensis (Wilson & Clifford, 1992). The sample taken from the plant in the tropical greenhouse exhibits a range of leaf angles (45-90 degrees) – not a very useful diagnostic character in this case! Our plant also exhibits glossy and alternate leaves which are spirally arranged.

The image on the left shows a retuse leaf apex where the mucron has fallen off and left a scar. The photo on the right shows the presence of two different sized serrate teeth. Both images attributed to Chris Reilly.

Our plant has small, serrate and dark green leaves. Some leaves are double-serrate and have a caducous mucron scar, which is a strong diagnostic indicator that the tea variety in the tropical greenhouse is Camellia sinensis var. sinensis: the China Tea Plant which is originally native to China (Wilson & Clifford, 1992).

Range and Cultivation

Camellia sinensis is a crop used by man for thousands of years, resulting in a rather skewed distribution. This makes calculating its original distribution in the wild incredibly difficult, with many suggestions likely to be little more than a guess (Sealy, 1958). The name sinensis literally translates ‘from China’, and the plant is believed to have evolved in the Eastern Himalayas, one of the most plant-rich and competetive ecosystems in the world. To survive the rigours of evolution, it has been suggested that Camellia sinensis increased the amounts of caffeine in its fruits to make them attractive to primates such as monkeys (Macfarlane & Macfarlane, 2003). It is interesting that another primate, Homo sapiens, along with other qualities should also rather enjoy the caffeine in tea; thus, increasing the range of Camellia sinensis considerably. Due to its relationship with man, this evolutionary quirk has offered Camellia sinensis gargantuan success at the species level.

Camellia sinenis prefers an equatorial and humid climate with annual temperatues of 18-20C; high and evenly distributed rainfall; and, at least 5 hours of sunshine per day. Similar to many other plants in the genus Camellia, soil is required with a pH of 4.5-5.5 along with good fertility, drainage and good layer of humus (Bonheure, 1990).

Tea Plantation: Note how the plant is maintained as a low growing shrub. This image is licenced under the Creative Commons Attribution-Share Alike unported licence. Image attributed to Martin Benjamin.

Today, most tea is grown in plantations, and is maintained as a low bush in a continuous phase of regenerative growth. Harvesting involves the process of mechanically or hand-plucking of the young shoots. Due to the chemical elements found in different parts of the plant, the best quality tea can be found in the young shoots. The production of black tea requires the oxidation and fermentation the Assam Tea Plant: Camellia sinesis var. assamica which is rich in flavanols. Green tea is produced by steaming or pan-firing the leaves of Camellia sinensis var. sinensis immediately after plucking. This process ensures the end product retains much of the desired chemical components (Wilson & Clifford, 1992).

An experiment! Preparing tea with Camellia sinensis leaves from the tropical greenhouse…

 History and Economic Importance

Tea is the most economicaly important member of the genus Camellia (Wilson & Clifford, 1992). We Britons collectively drink 165 million cups of tea a day (Macfarlane & Macfarlane, 2003). It is estimated that more than 3.6 million tons of tea leaves are produced annually in 40 countries (Lu et al. 2012). Besides being a delicious hot beverage, there appears to be a number of health benefits associated with drinking tea. Antioxidant compounds found in abundance in the leaves of green tea such as flavanols and polyphenols, could provide potential benefits in the treatment of conditions such as cancer, diabetes, obesity, and many cardiovascular ailments. The next time you have a cold, it may be useful to bear in mind that green tea-leaves have a comparable vitamin C content to that of a lemon! (Vijayan et al. 2009).

In the UK, tea-drinking is socially and culturally intertwined within the British consciousness. This ubiquitous and everyday occurrence shrouds what can best be described as a somewhat unpleasant and chequered history…

In 17th century Britain there were no taps with clean running water; the only ways of producing clean, disease free water were to sterilise it through boiling, or produce alcoholic beverages such as ales. Unsurprisingly, the consumption of alcoholic drinks did little to boost productivity amongst the masses! Boiled water must have been a rather dull alternative. The introduction of tea in 1652 provided a highly pleasant flavouring to boiled water; its popularity exploded amongst all classes in society (Hobhouse, 1999).

The cost of a cup of tea: the annihilation of an empire

Opium Wars 1840-42. Image sourced from Wikimedia Commons. This image is in the public domain because its copyright has expired.

The British imported vast amounts of tea for 150 years via the Chinese port of Canton. Despite the trade of tea at one point representing as much as 5% of GDP, the British had little idea of what a tea-plant looked like, let alone anything about tea husbandry. Rich in resources and technologically advanced, the Chinese saw little reason to fully engage with the West, and were happy with their tea trade monopoly. Somewhat frustrated with the stance of the Chinese, the British decided to ‘open’ China up to trade, resulting in the Opium wars of 1840-42. Some of the British tactics could be described as dubious at best: one such tactic included the mass sale of opium, grown and smuggled from India, and then sold on to the Chinese populous. This resulted in a cash bonanza for the British, but corruption and social disintegration within China. British victory resulted in the near annihilation of Chinese culture; but the acquisition of Hong Kong and tea husbandry for the British. From the 1840’s onwards, tea husbandry in the field was no longer a secret with new, more efficient plantations appearing in British ruled India. (Hobhouse, 1999).

Tea, Taxes and the American Revolution

The Boston Tea Party! This image is sourced from Wikimedia Commons. This image is in the public domain because its copyright has expired.

In 1773 the British introduced a piece of legislation which sought to add a small tax levy of 3 pence to the pound on all tea sold in the colonies of America. This caused outrage amongst the colonists, as this tax constituted ‘taxation without representation’. This piece of legislation culminated in ‘the destruction of the tea’ on 16th December 1773; men disguised as Mohawk Indians boarded three ships in Boston Harbour and through an entire tea cargo into the water. This event is now remembered as ‘The Boston Tea Party’ and proved to be a key event in the escalation of the American Revolution. Since American independence, tea has become a decidedly un-American drink. It’s interesting to note that Canada, which remained loyal to the British, consumes 4 times as much tea per head than America (Hobhouse, 1999).

References

Bonheure, D. (1990). Tea. London & Basingstoke: Macmillan Education Ltd.

Heywood, V. H., Brummit, R.K., Culham, A. & Seberg, O. (2007). Flowering Plant Families of the World. Ontario, Canada: Firefly Books.

Hobhouse, H. (1999). Seeds of Change: Six plants that transformed mankind. London & Basingstoke: Macmillan Publishers Ltd.

Lu, H., Jiang, W., Ghiassi, M., Lee, S., & Nitin, M. (2012). Classification of Camellia (Theaceae) species using leaf architecture variations and pattern recognition techniques. PLoS One. 7(1): e29704.

Macfarlane, A. & Macfarlane, I. (2003). Green Gold. London: Edbury Press.

Prince, L.M. (2007). A brief nomenclatural review of genera and tribes in Theaceae. Aliso, 24, 105-121.

Sealy, J. R. (1958). A Revision of the Genus Camellia. London: The Royal Horticultural Society.

Stephens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 12, December 2012. http://www.mobot.org/MOBOT/research/APweb/.

Vijayan, K., Zhang, W., & Tsou, C. (2009). Molecular taxonomy of Camellia (Theaceae) inferred from nrITS sequences. American Journal of Botany, 96, 1348-1360.

Willson, K. C., & Clifford, M. N. (1992). Tea: Cultivation to Consumption. London: Chapman & Hall.

Copyright Statement

Permission granted to reproduce for personal and educational use only. Commercial copying, hiring and lending is prohibited.