Poinsettias are the most popular flowering, potted plant in North America. Have you ever wondered why they seem to be everywhere during the holiday season, but scarce during the rest of the year?
Name Calling
Poinsettias, or Euphorbia pulchirrima, belong to a large group of plants called spurges. Poinsettias grow as a perennial shrub in Mexico and parts of Central America. The Aztecs called the shrub Cuetlaxochitl and used it to produce a reddish-purple dye, as well as using the latex sap for treating fevers. Mexicans call it Flor de Noche Buena, or Christmas Eve flower. Joel Roberts Poinsett, the first US Ambassador to Mexico and avid botanist, introduced the plant to botanical friends in 1828 and later, historian and botanist, William H Prescott named the plant after Poinsett. In the 1920s, Paul Ecke, in southern California, began to cultivate and promote poinsettias as indoor ornamental plants for Christmas.
Colouring In
The conspicuous colourful parts of the poinsettia are not part of the flower, but modified leaves called bracts. The bracts change colour by gaining anthocyanin pigment as the nights get longer after the autumnal equinox. You can trim the bracts and get them to turn red again next year, by keeping them in total darkness for about fourteen hours each day for about eight weeks. The flowers are the yellow bits in the middle called cyathia. If you choose ones where the yellow part has not opened yet, then the plant will last longer, because poinsettias tend to drop their leaves once the pollen is done.
Reasons to Change
More than a hundred varieties of poinsettias now exist and the one in my living room is small, but bushy, with more flowers, different colours and longer-lasting leaves than its wild ancestor. The pigment in the red bracts may be more effective at photosynthesis at lower light levels. Down south, the amount of daylight does not change that much during the winter, but the climate does get cooler and drier. Perhaps potential pollinators, such as hummingbirds, green bees, butterflies and sphinx moths—who all have tongues long and skinny enough get at the nectar, are thirsty and hungry and the main point of the red bracts is to help attract them to the plant.
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