Today's photographs are courtesy of Ana Margarida Silva of Portugal, who sent them along as a season's greeting to everyone who contributes to Botany Photo of the Day, including readers, commenters, photographers and writers. Claire wrote today's entry:
For a holiday theme, today's post will be about the well-known Euphorbia pulcherrima of the spurge family, Euphorbiaceae. The poinsettia! Called Cuetlaxochitl by the Aztecs, the poinsettia is a native to Mexico and Central America and has been used by humans for centuries before 16th century legend linked the species to Christmas. The Aztecs used Euphorbia pulcherrima as a red dye (from the floral bracts) and also medicinally for reducing fever (antipyretic, much like aspirin). The true inflorescence--a cyathium--is small and grows in the centre of the richly-coloured bracts.
Euphorbia pulcherrima has a long history as a Christmas flower before it was brought to North America in the 19th century by Joel Roberts Poinsett, the Mexican ambassador for the United States. In Mexico, the flowers of the species are sometimes called Flores de Noche Buena (Flowers of the Holy Night -- Christmas Eve). The legend behind this name and its symbolism stems from a story about Pepita, a young Mexican girl, who had nothing to offer as a gift for the birthday of Jesus. Pepita was told by an angel to bring roadside weeds to the church, and as she lay her humble gift on the altar, the weeds miraculously bloomed large red flowers.
The poinsettia is a very popular plant commercially during the holidays (almost all are sold within the six weeks before December 25). A near-monopoly on commercial production existed until the early 1990s in the USA due to a production secret. Euphorbia pulcherrima requires a strict light schedule and temperature regime to produce the vividly coloured bracts, but this wasn't a secret in comparison to how to produce consistent, compact flowering plants. The grafting technique to do this is no longer secret, though, and production has now shifted to parts of the world where labour is less expensive.
If you are worried about poisoning, the tales of toxicity are untrue. Euphorbia pulcherrrima is a mild irritant to the skin and stomach. Copious amounts of leaves ingested would only produce minimal symptoms and discomfort.
Wikipedia has more information on cultivation and images of the many varieties of poinsettia which can come in nearly any color in the wild (except blue or purple) and are cultivated in white, red and pink (though red, unsurprisingly, is the most popular).