This series of posts will highlight the plants that help you celebrate the Yuletide season.
Today we’re talking poinsettias. How many facts do you know about the flower? First of all, poinsettias are known by many names. The Latin name Euphorbia pulcherrima translates as ‘most beautiful.’ They were first known as Cuetlaxochiti by the Aztecs in their native Mexico. Today they are known as “La Flor de Noche Buena” or Christmas Eve flower. We call them poinsettias in America because they were first introduced to the United States in 1825 by Joel Roberts Poinsett, the first Minister to Mexico.
While we’re on the subject of nomenclature, what we normally think of as poinsettia flowers aren’t really flowers at all. Here’s your plant science word of the day: bract. They may look like colorful petals, but they are actually specialized leaves associated with the much smaller ‘actual poinsettia flowers’. The fortuitous combination of intense color with seasonal timing has led to the popularity of poinsettias at Christmas. The biology behind this timing involves short day photoperiodism. Remember the other day when I told you that plants know the day of the year by measuring the length of the night? That’s exactly what poinsettias do. Since they are a short day photoperiod plant, when the night is sufficiently long, a biochemical response is triggered to turn the bracts vivid colors.
The colorful bracts remain until the small yellow flowers* are pollinated, then the plant sheds them along with most of the other leaves. From the plant’s perspective, once pollination and seed production occurs, its work is done, and there is no need to keep up such showy attire. I’m sure many people just assume that they have killed their potted poinsettias by this point in their captivity, but that’s not always the case. You can keep your poinsettia plants alive for another round of flowering next Christmas season. Check out this link for the best cultural practices to do so. Just remember, whatever strategy you decide to use to induce coloration (cardboard box or enclosed room) make sure that you really give them 12 – 15 continuous hours of darkness. The plant will know if you open the door to the room or turn on the light in the closet to stash a Christmas gift.
Some of you may only want to tolerate your poinsettias for a single season, if that, because of the rumor that these plants are poisonous to people and pets. This is actually false. While they are not edible and ingestion may cause your pets and toddlers to yack all over your Christmas tree skirts, they are not toxic. Your pets and plants would have to ingest hundreds of bracts to cause death. The ancient Aztecs used the latex produced by the plant as a fever reducer. Of course, these plants are to be enjoyed for their visual aesthetics only, so it’s always safest to keep them out of tasting reach of your children and pets.
The majority of poinsettias are purchased during the six weeks leading up to Christmas, and they are big business in the floral industry. They account for ~$250 million in sales annually and are top the list in market value for potted plants. This big business means that this plant has been modified significantly from its wild form in order to please Christmas customers. The wild version of Euphorbia pulcherrima is a shrub that reaches heights of 8 – 10 feet! Researchers initially enlisted the help of plant growth regulators to yield a more compact plant structure suitable for indoor potted plants. Subsequently, breeding programs took advantage of some favorable genetic finds for superior poinsettia plants. Perhaps one of the most significant traits was bract retention. Instead of immediately dropping the bracts and leaves after color development as the plants are naturally inclined to do, the ‘Ruff and Ready’ cultivar retains its bracts and leaves for the length of the holiday season and is the parent stock of many varieties available today. And today, there are more than 100 varieties of poinsettias that differ in bract size, shape and color. Colors include just about every hue of the traditional red, to pink, to cream to combinations of all of the above in double tones and speckles. The Ecke family pioneered the commercial cultivation of poinsettias, and their catalogue is overflowing with examples of their breeding success stories.
More recently, USDA-ARS researchers have uncovered the biological agent responsible for generating the desirable dwarfed poinsettia plant stature without the use of expensive growth regulators. The answer was surprising- phytoplasma, an infectious agent found within some plant varieties. These bacteria are usually pathogens, but in the case of poinsettias, they actually produce a trait desirable for commercial sales. Earlier this year a similar poinsettia branching plant type was achieved by making a transgenic poinsettia expressing an Arabidopsis gene AtSHI, which alters the internal hormone balance to change plant structure. Other scientists are focusing on the diseases that attack these valuable plants. Still others are working on reducing the energy costs associated with commercial production of these plants. Poinsettias may show off their colors during the long nights of winter in the Northern Hemisphere, but they decidedly prefer warmer temperatures than those available outdoors during North American winters. This means that growers must keep the heat on inside greenhouses while the plants are getting ready for market. Energy costs have increased by 230% over the past decade, which means slimmer profit margins for poinsettia growers. Researchers have reported that some varieties can stand slightly colder temperatures while still yielding high quality plants in time for the Christmas season. They just have to start their seedlings just a little bit earlier in August. This timing adjustment in combination with the proper choice of cultivar will ultimately save energy costs for growers.
So enjoy your poinsettias for a little while longer this season. Then, when all the bracts and leaves fall off, and your family starts to ridicule your plant care-taking skills, you can impress them with your new botanical knowledge. “Well, no it isn’t my fault. That’s just what poinsettias do after they have flowered for several weeks. I’ll just prune them back and re-train them to a short day photoperiod for beautiful bract blooms next year.” Walk away as they pick their jaws up off the floor. They’ll be too stunned to ask you when was the last time you watered it (um, never?). Plus, I won’t tell anyone that you left it out overnight during a frost. Just discreetly buy another poinsettia next year, and if anyone asks how the re-blooming project went, just blame failure on your dog/cat/child/incompetent summer house-sitter and move on. If you do manage to get your plant to bloom for the next season, give yourself a gold star from me and be sure to rub it in everyone’s noses as they visit your home for the holidays. One-upping the people we love the most with picture-perfect traditions is what the season is all about anyway, right?**
*Playing Christmas trivial pursuit? What color are poinsettia flowers? Answer: Yellow. Those that answer red or pink or cream etc. can wallow in their wrongness.
**That’s sarcasm. I know it isn’t. No need for well-meaning, but nonetheless pompous comments below.
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