Natural History of Holiday Plants Exhibit
Evergreens | Holiday Color | Poinsettia | Holly | Mistletoe
Christmas Cactus | Christmas Tree | Common Holiday Plants
For a variety of reasons different colors such as red, green, blue, and silver have become part of the festive decor of the holiday season. Two of the most common colors, red and green, are frequently exhibited by the plants used during this season such as Poinsettias, Christmas Cactus, and holly. The colors of plants are associated with different functions of different plant organs. For example, the red coloration of many flowers helps to attract particular pollinators in order to carry on sexual reproduction. In our region, the red, tubular flowers of the Ocotillo (Fouquieria splendens) and Chuparosa (Justicia californica) are attractive to various species of hummingbirds, which efficiently relay pollen from one plant to another. The green color in most leaves, and even in some stems of plants like cacti, is usually associated with the process of photosynthesis. This chemical reaction is how most plants use the sun's energy in order to make sugars, and incidentally produce the oxygen that we breathe.
What makes plants red?
The red, pink, violet, magenta, and blue colors in many flowers and other plant parts are due to the presence of various plant pigments. The colors found in Poinsettia, holly, and most flowering plants are produced by water-soluble flavonoid compounds called anthocyanins. However, in a small, related group of plant families in the order Caryophyllales (Carnation order), there are other similarly colored plant pigments called betalains, which are synthesized via a different chemical pathway. Betalains get their name from red beets (the genus Beta in the Chenopodiaceae), which are red in color due to the presence of the betalain. Certain betalains are responsible for the reddish flowers in another favorite holiday plant, the Christmas Cactus (Schlumbergera bridgesii). The discovery of betalains in cacti helped taxonomists understand the phylogenetic position of the Cactus family or Cactaceae. The Cactaceae were once classified in their own order near the carrot family (Apiaceae), but now the family is placed in a very different order, the Caryophyllales, along with the only other betalain-producing angiosperm families such as: Achatocarpaceae, Aizoaceae (with ice plants), Amaranthaceae, Basellaceae, Chenopodiaceae (with red beets and saltbushes), Didieriaceae, Nyctaginaceae (with Bougainvillea), Phytolaccaceae (with Pokeweed), and Portulacaceae.
What makes plants green?
The basic green coloration of plants is caused by the pigment chlorophyll. Chlorophyll pigments are light energy-capturing molecules that play an essential role in the primary events of photosynthesis. Slight chemical variations in the basic structure of chlorophyll produce different types of chlorophyll (a and b) that are specific for certain wavelengths of light. Both chlorophyll a and chlorophyll b absorb light energy in the red and blue portions of the visible light spectrum. Therefore, the yellow-green portion of the visible spectrum is not absorbed but is reflected, and the human eye perceives it as green. So the next time you look at the green boughs of holly with which we deck our halls, try to remember that "what you see is what you get," but that is not necessarily what the plants get.
Continue to Poinsettia
Text by Jon P. Rebman, Ph.D., Curator of Botany;
Calliandra californica (left) and Fouquieria splendens (right, Ocotillo)
photos courtesy of Norm Roberts