The poinsettia is native to South and Central America. Its roots have given this plant a plethora of mythological, historical and political stories to tell you about. If you would like to learn more about this aspect of poinsettias, see my supplementary article, The History of the Poinsettia.
The breeding of poinsettia stock is a very big business in Europe and North America. Every summer, rooted stocks and cuttings of the most popular types are shipped to growers all over the world. Then comes the process of growing these small plants on to the size they attain at Christmas-time. By September, poinsettia growers are ready with their black-out sheets, which cover the entire poinsettia crop and supply them with the exact amount of daylight and complete darkness they need in order to flower. Hormonal growth inhibitors are used in precise levels on the plants. These keep them compact. Before the discovery of these hormones, poinsettias were a gangly mess, breaking branches with each movement. Those of you who have been doing Christmas for longer than 40 years may remember. Breeding has improved the form of the poinsettia also, and produced many amazing colours as well.
Poinsettias begin the flowering process when they sense that light levels are diminishing. When the night is 14 hours long, the plant concentrates its energy on producing flowers. Once the flowers develop, but before they are open, thinner leaves develop at the top of the plant, and turn red, or the colour of the variety. These are known as bracts, which are not flower petals in any way. Nor do the bracts serve any sexual function. Thus, they are not a part of the flower. The role of the bract is to attract pollinating insects to the poinsettia during the flowering period. In the wild, the redder the poinsettia, the more insects it attracts.
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