By Waheed Arshad
With UK supermarket shelves currently full of poinsettia (Euphorbia pulcherrima), it can only mean one thing – Christmastime is upon us, and the traditional ornamental plant returns to our lives once more.
Cuttings, first planted in July, have been carefully nurtured to the point of perfection by expert horticulturalists, striving to bring poinsettia to their festive peak. Its distinctively-coloured bracts (not leaves) range from the usual red, to white, orange, or even marbled peach. The variety of colours is determined by levels of pigments known as anthocyanins. Predominant in tea, wine, and berries, anthocyanins are members of the flavonoid group of phytochemicals which have diverse roles in UV protection, metal ion regulation, and responses to nutrient deficiency1,2. Poinsettia bracts are often mistaken for petals because of their colour and arrangement near the tiny, pale yellow flowers (a cluster of cyathia). In fact, poinsettia bracts are actually modified leaves aggregated at the branch extremities, thought to have evolved as an adaptation to attract pollinators.
Understanding the process of bract pigmentation is the subject of much research, primarily for the breeding potential of new cultivars with improved horticultural and aesthetic traits3. Warmth, blacked-out growing conditions, and a perfect watering regime are key to successful poinsettia pimping. Plants must experience a 14-hour period of total darkness, per day, for a period of around three months, and then need to be introduced to an increasing amount of daylight. This growing process, known as photoperiodism, is naturally triggered in winter by shorter day lengths and drier weather, coaxing poinsettia bracts into their vibrant colours.
During bract development under short-days, the plant stops producing chloroplasts, absorbs fewer nutrients, and reduces the rate of photosynthesis4. This triggers the production and accumulation of anthocyanins in the bracts (akin to what we see in the leaves of autumnal deciduous trees). During growth, any disruption in light quantity and quality can have a dramatic impact on the overall crop, meaning poinsettia production can be a risky business. In fact, with rising costs of heating crops, coupled with decreasing retail prices, some UK growers have reduced their production.
Nevertheless, as is the case for many culturally significant plants, the poinsettia has an interesting backstory and popularity extending further than you might think. Native Aztecs referred to it cuetlaxochitl (“brilliant flower”), and used its bracts to make a red-purple dye. Additionally, its secretions of sticky, milky-white latex were used as a medicinal treatment for fevers. Native to hot, dry areas of Mexico and Central America, the shrub can flourish up to 3–4 m (10–13 feet) tall. Because the poinsettia’s sensitivity to temperature excludes it from the high altitudes of Mexico, the last Aztec king, Montezuma (1480–1520), is thought to have had it imported from other regions to adorn his palaces in the 16th Century.
Around the 17th Century, Franciscan priests started incorporating poinsettias into the Fiesta of Santa Pesebre nativity procession. It seemed only natural to use a plant species that flowered during the festive season. The common name is derived from Joel Roberts Poinsett*, US ambassador to Mexico, who brought it back from his travels in 1825. Since then, plant breeders have cultivated the poinsettia into a more colourful, compact and floriferous form, making it the renowned Christmas plant it is today.
Whether your home is of a traditional or modern aesthetic, the poinsettia is a versatile addition to any colour scheme. Flowering (or “bracting”) time is around four to six weeks, and once the festive period has passed, the poinsettia will start to lose its leaves and enter a dormant state. Battling to keep it alive for the next winter requires patience and diligence, particularly from September/October onwards where artificial growth conditions are required for the perfect bract colour. Returning them to former glory seems like a nigh impossible task best left to the experts – maybe a poinsettia is just for Christmas after all?
* One for your diary – “Poinsettia Day”, next week, December 12th, marks the death of Joel Roberts Poinsett in 1851.
1. Landi M., Tattini M., and Gould K.S. (2015) Multiple functional roles of anthocyanins in plant-environment interactions. Environmental and Experimental Botany 119: 4–17. DOI: 10.1016/j.envexpbot.2015.05.012
2. Tanaka Y., Sasaki N., and Ohmiya A. (2008) Biosynthesis of plant pigments: anthocyanins, betalains and carotenoids. The Plant Journal 54: 733–749. DOI: 10.1111/j.1365-313X.2008.03447.x
3. Slatnar A., Mikulic-Petkovsek M., Veberic R., Stampar F., and Schmitzer V. (2013) Anthocyanin and chlorophyll content during poinsettia bract development. Scientia Horticulturae 150: 142–145. DOI: 10.1016/j.scienta.2012.10.014
4. Kannangara C.G. and Hansson M. (1998) Arrest of chlorophyll accumulation prior to anthocyanin formation in Euphorbia pulcherrima. Plant Physiology and Biochemistry 36 (12) 843–846. DOI: 10.1016/S0981-9428(99)80001-1