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Holiday Plants

Evergreens        Holiday Color         Poinsettia           Holly        Mistletoe          Christmas Cactus        Christmas Tree

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Many of the sights, smells, and tastes associated with the holiday season are directly due to various plants and their products -- brightly decorated trees, evergreen wreaths bearing pine cones, sharply contrasting colors of red and green Poinsettia leaves, sprigs of mistletoe hanging in doorways, and warm fires burning in a hearth. Even the cotton (Gossypium spp.) used in new clothes or stockings hung on the mantle, and wood pulp for giftwrap are products derived from plants.

But don't forget that many of our holiday smells and tastes are also of plant origin. Where would we be -- other than twenty pounds lighter -- without certain plants for special holiday treats? If we did not have wheat (Triticum aestivum), there would be no flour for cookies; without corn (Zea mays), no tamales. Without plants there would be no cacao or chocolate (Theobroma cacao) for fudge, no sugar from sugar cane (Saccharum officinarum) or sugar beets (Beta vulgaris) for candies or cakes, no ginger (Zingiber officinale) for gingerbread, no fruit for fruitcake, no peppermint (Mentha piperita) for candy canes, no mulling spices (various combined species) for wassail, and no cinnamon (Cinnamomum zeylanicum) flavors. I think we could safely say that it would be a little less lively to toast a new year with good cheer without various alcohols and liquors which come from an array of different plants.

There is no question that plants and their products are used by all of us every day and for special times of the year. Our winter holiday season is especially abundant with plants that symbolize various values and virtues that have been adopted over the years by different cultures in different ways. Let us take a look at some of the natural history that surrounds just a few of these plant species that accent our lives and help to create our holiday ambiance.

No matter what reason you may celebrate the holiday season, there are a wide range of plant species that are commonly used to help to signify and beautify this time of year. Some of the plants have traditional usages that date back to earlier cultures, such as evergreen trees symbolizing long life and hope. But other holiday plants have been adopted more recently in the New World, such as decorating with Poinsettias and Christmas Cacti. 

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Evergreens

Since evergreens have foliage throughout the year, they seem almost unchanging -- it is no wonder that so many of them have been revered by cultures as a symbol of strength and life. The idea of an evergreen plant may give you an image of eternal life, but in a simpler sense it is a reminder of spring. In temperate climes, evergreens exhibiting fresh greenery help to liven up the darker days of winter and the gray tones of a leafless landscape.

What is an evergreen?

Botanically, it is defined as a woody, perennial plant with foliage that persists and remains green throughout the year. The term "evergreen" usually opposes the term "deciduous" in botany. A deciduous plant is one with foliage that falls off or is shed at a specific season or stage of growth. A common example of a "drought deciduous" plant in our deserts is the Ocotillo (Fouquieria splendens). This plant grows leaves whenever there is enough moisture available, but it quickly drops these leaves in order to conserve its water whenever conditions are very dry. The Ocotillo can grow leaves and also drop them many times a year, if conditions warrant it.

Do evergreens lose their leaves?

Yes! Evergreens seem apparently unchanging, but they do lose their leaves over time. Although it may not be as noticeable as a deciduous plant that loses all of its leaves at a particular time of the year, most evergreens are continually shedding and replacing a few leaves at a time.

Can you think of a local, native, evergreen plant?

In our region we have many different species that are evergreen. Along the coast you can commonly see the broad green leaves of the Lemonadeberry (Rhus integrifolia) or the laurel-like leaves of Laurel Sumac (Malosma laurina) throughout the year. Another common plant species with obvious evergreen leaves that can be spotted in most of our urban canyons is the Spanish Bayonet or Mohave Yucca (Yucca schidigera). In our higher mountains of the region, there are various conifer species such as pines and junipers that are obvious examples of evergreen foliage. 

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Poinsettia

Scientific name: Euphorbia pulcherrima
Plant family: Euphorbiaceae (Spurge family)
Other common names: Christmas Flower, Cuetlayochitl (by the Aztecs), Lobster Flower, Flame-Leaf Flower, Flor de Noche Buena ("Flower of the Holy Night," i.e., Christmas Eve)

The plant that is responsible for the majority of commercial plant sales during the holiday season in our region is the Poinsettia. This species is a perennial shrub with white milky sap that can grow up to six feet (2m) tall and is native to Mexico. The Poinsettia is usually classified in the genus Euphorbia subgenus Poinsettia, although some taxonomists recognize this subgenus at the generic level so you might occasionally see the scientific name as Poinsettia pulcherrima. Although Euphorbia pulcherrima is not native to our region, in the southern part of Baja California Sur there is another closely related species (Euphorbia cyathophora) that looks somewhat similar to the cultivated Poinsettia by having reddish-colored bracts surrounding the flowers. This weedy species commonly occurs in the eastern and central United States, Mexico, and Central America.

The Poinsettia is named in honor of Joel Robert Poinsett, an American ambassador to Mexico who introduced this plant species to the United States in the 1820s by bringing cuttings from Mexico back to his greenhouse in South Carolina. Although Poinsettias are used now mainly for decoration, the sap has been used by some cultures to control fevers, and the floral bracts were once used to make a reddish dye.

In order to induce this plant species to flower, at least a few weeks of more than 12 hours of darkness each day are required. Therefore, commercial growers have to "fool" the plant in greenhouse conditions by artificially manipulating the length of daylight and darkness periods in order to get the plants in a flowering state during our holiday season.
A flower or not a flower? That is the question...

Flowers are not always as they appear to be. Generally, we tend to think of pretty blooms as individual flowers, no matter what their size. However, sometimes what appears to be a single flower may actually be a grouping of smaller flowers that together look like an individual flower. Some of the best examples of this arrangement exist in the Asteraceae (Compositae), the Sunflower or Daisy family. Some composite "flowers" actually have two different types of flowers making them up. For example, if you think of what a common Sunflower (Helianthus annuus) looks like, the yellow outer petal-like structures are each individual flowers called ray flowers, and the many brown structures in the center are also individual flowers called disk flowers. So the next time that you start pulling off "petals" of a daisy and chanting "he loves me, he loves me not," realize that you are actually pulling off individual flowers and not petals, as you may have thought.

This same general concept can also be encountered in Poinsettias, but it is even a bit more derived. The most conspicuous parts of the Poinsettia "flower" are brightly colored (usually red) bracts, which are actually modified leaves. In the center of these circles of bracts are several smaller greenish structures that are grouped together. Each one of these structures, called a cyathium or pseudanthium, is actually a small grouping of individual flowers that lack petals and have only one sex (staminate = male or pistillate = female). Therefore, unlike most composite flowers, individual flowers in Euphorbia species do not have their own petals.

It should be noted that not all Poinsettias have red bracts. Different cultivated varieties of Poinsettias have varying bract colors including pink, white, or green. 

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Holiday Color

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. 

Holly (Ilex opaca)

Holly

Scientific name: Ilex opaca (New World) and Ilex aquifolium (Old World)
Plant family: Aquifoliaceae (Holly family)
Other common names: American Holly, English Holly, Christmas Holly

Holly is a plant frequently utilized to "deck our halls" during the holiday season. The boughs used to decorate typically are cuttings from any evergreen trees or shrubs in the genus Ilex. The most common holly species used are Ilex opaca from the eastern United States and Ilex aquifolium from Eurasia. Both species have spiny-margined, evergreen leaves, and usually exhibit red berries.

Are male or female holly plants most often used in holiday decorating?

If you are decorating with holly that has red berries, then you are using pistillate "female" plants. Many holly species are dioecious, which means that staminate "male" and pistillate "female" reproductive organs are separated on different individual plants. This sexual condition (dioecy) with individual plants bearing separate sexes promotes cross-fertilization, or outcrossing, which increases the genetic variability of the species but usually at the cost of lower seed-setting efficiency. Dioecy also prevents isolated individuals from reproducing on their own most of the time. Therefore, in most cases it is necessary that male and female plants grow in close proximity, or no red berries will be produced on the female plants for use during the holidays.

The Desert-Holly ( Atriplex hymenelytra ) that commonly grows in Anza-Borrego Desert State Park and in northeastern Baja California is not closely related to the holly (Ilex spp.) used during the holiday season. Although their common names suggest a close relationship, the name refers to its sharply-toothed leaves. Desert-Holly is a saltbush in the Chenopodiaceae (Goosefoot family) that is actually more closely related to beets (Beta vulgaris) and pickleweeds (Salicornia spp.) than to the evergreen decorative holly.

In the Cape region of Baja California Sur, there is a species of holly ( Ilex californica ) that can be found naturally occurring in the Sierra de la Laguna. 

Mistletoe (Phoradendron densum)

Mistletoe

Scientific name(s): Viscum album (Old World), various Phoradendron spp. (New World), especially Phoradendron macrophyllum in San Diego County
Plant family: Viscaceae (Mistletoe family)

Mistletoes are perennial, flowering plants that are parasitic on aboveground parts of woody trees and shrubs. Mistletoes have specialized roots with the ability to penetrate a host plant and absorb nutrients. Most mistletoe species are either full parasites like dwarf mistletoes (Arceuthobium spp.) or partial parasites, called hemiparasites, like the mistletoes (Viscum and Phoradendron spp.) used for holiday decoration. Hemiparasites get a portion of their nourishment from their host, but they also contain chlorophyll, making them green and giving them the ability to conduct photosynthesis and make some sugars for themselves. The berries of most mistletoe species are white, but they can also be yellowish or even pink to red. Most parts of a mistletoe plant are toxic and should not be eaten.

In Europe, the species of mistletoe most frequently used is in the genus Viscum (Viscum album), but in the New World various species in a different genus in the same family, Phoradendron, are used. In San Diego County, we have six different species of mistletoe (Phoradendron spp.) and two species of dwarf mistletoe (Arceuthobium spp.). The most commonly used species during the holidays in our region is the Big Leaf Mistletoe (Phoradendron macrophyllum), which is parasitic on various riparian trees and shrubs including sycamores, cottonwoods, willows, and alders.

How do mistletoe seedlings get up in tall trees or spread from one host plant to another?

Some mistletoe species have explosive berries that can propel their sticky seeds outward for some distance, giving them the opportunity to come in contact with branches or treetops away from the mother plant. However, most often the mistletoe berries are eaten by birds that fly from tree to tree and the ingested seeds pass through the digestive tract and are expelled in fecal matter. Frequently, this bird excrement lands on the branches of trees where birds perch. The mistletoe seeds can then germinate in a new place and penetrate the host plant. It is believed that the common name "mistletoe" was derived from this method of seed dispersal. The origin of the word "mistletoe" appears to come from the Anglo-Saxon (Old English) words "mistel" which means dung and "tan" for twig. Thus, mistletoe literally means "dung-on-a-twig."

Why are mistletoes used during the holidays?

Throughout history and in many different cultures, mistletoes have been a source for many concepts, symbols, and rituals. Probably due to their parasitic nature, elusive method of dispersal, and strange growth habit, many cultures have revered, feared, or thought them to have magical properties. As a result, mistletoes have been interpreted in varying ways such as: symbols of fertility and romance; aphrodisiacs; bestowers of life; protectants against poisons, witches, or evil spirits; and even plants of peace under which opposing groups can make truces. The act of kissing under a sprig of mistletoe may date way back to the Greek festival of Saturnalia where it was believed to confer fertility. But, no matter what symbolism you may interpret with mistletoes, they all exhibit a fascinating life history and are an interesting part of our natural, botanical world.

Is there any mistletoe etiquette?

Correct etiquette says that a person should pluck a berry from the mistletoe branch each time they kiss under it, and when there are no more berries left on the plant, there should be no more kissing. (Please note, if you are going to follow this suggestion, you should buy a larger bag of mistletoe this year from our Museum's Canyoneers at Balboa Park's December Nights!)

Christmas Cactus (Schumbergera x buckleyi)

Christmas Cactus

Scientific name(s): various Schlumbergera (Zygocactus) species or cultivated hybrids, especially Schlumbergera x buckleyi
Plant family: Cactaceae-Cactus family
Other common names: Orchid Cactus

The Christmas Cactus is a succulent perennial which lacks spines and is native to the South American tropics of Brazil. Like many tropical cacti, this holiday favorite is an epiphyte, which means it lives on other plants. Unlike a parasitic plant that obtains nutrients from its host, epiphytes just use their host as substrate, a place to live.

The genus (Schlumbergera) to which the Christmas Cactus belongs is one of the most widely cultivated and enjoyed groups of cacti in the world. They have been extensively hybridized by artificial means in order to produce a wide range of different colored flowers, including magenta, white, pink, salmon, and orange. The closely related Thanksgiving Cactus or Crab Cactus (Schlumbergera truncata, syn. Zygocactus trucata) is also common in horticulture and may even be one of the parent species of the hybrid Christmas Cactus. The showy flowers produced by these cacti are pollinated in nature by birds.

Do Christmas Cacti have leaves?

The green, flattened, leaf-like structures that make up the majority of a Christmas Cactus are actually modified stem segments called cladodes. The stems of our local species of prickly-pears or nopals (Opuntia spp.) are also called cladodes since they too are flattened and leaf-like. In most cacti, the leaves have been modified into spines which have many different functions for the plant, or as in the Christmas Cactus, the leaves and spines are absent.

What does day length and darkness have to do with holiday flowers?

Various plant species require cues from the environment to regulate the timing of certain events, like flowering. This mechanism called photoperiodism occurs when plants initiate flowering or other activities in response to relative lengths of daylight and darkness. In winter, the days get shorter and the nights get longer. This is a very important indicator to some plant species, e.g., Christmas Cactus, Poinsettia, and some Chrysanthemum species, to stimulate them to start flowering. In these species it is actually the longer period of darkness, not the brevity of light, that seems to be important in helping them to recognize their appropriate flowering times. Commercial growers have been able to manipulate flowering times by artificially changing light regimes in greenhouse settings in order to induce plants to flower at a particular time of the year, e.g., Poinsettias in bloom during the holidays. Although many of our favorite holiday flowers are "short-day" plants since they require at least 12 hours of uninterrupted darkness to stimulate flowering, it should be noted that some plants are "day-neutral" and are capable of flowering regardless of the amount of light (or darkness) they receive each day. In these species, flowering is controlled by other factors.

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Christmas Tree

Scientific name(s): various species of Abies, Pseudotsuga, Pinus, Juniperus, etc.

Plant family: usually Pinaceae-Pine Family or Cupressaceae-Cypress Family

Other common names: tanenbaum; or fir, pine, cedar, etc. depending upon the species

Many species of conifers are used as Christmas trees, with the choice of species for any household being influenced by personal choice and by what trees are available locally. The first Christmas trees were probably firs (Abies), but now in the United States, Douglas Fir (Pseudotsuga menziesii), pines (Pinus), cedars and junipers (Juniperus) may be used. However, there are many alternative choices to these conifer species depending upon local tradition and the region where you live. Even mesquites (Prosopis), century plant stalks (Agave), Elephant Trees/Torotes (Bursera), rosemary (Rosmarinus officinalis), and plastics (artificial trees) have been used.

What do Christmas trees and local drought-tolerant shrubs have in common?

Most Christmas trees are cone-bearing (conifer) plants that frequently have modified leaves that we refer to as needles. These needle-like leaves have various adaptations like thick, waxy outer layers that help the plant to conserve water, and resin canals that help to protect the leaves from damage due to cold, icy temperatures. In general, evergreen plants in temperate climes must have various survival adaptations in order to cope with more than one type of environmental stress. Like ornamental Christmas trees, many of our local evergreens including Chamise (Adenostoma fasciculatum), Buckwheat (Eriogonum), and our mountain conifers have adaptations to help retain water during the unfavorable times of the year, such as winter at high elevations and dry summers near the coast in our Mediterranean-type climate.