San Diego Natural History Museum--Your Nature ConnectionSan Diego Natural History Museum Biodiversity Research Center of the Californias: Botany Department


Plant Atlas
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Field Guide

Natural History of Holiday Plants Exhibit
Evergreens | Holiday Color | Poinsettia | Holly | Mistletoe
Christmas Cactus | Christmas Tree | Common Holiday Plants


Poinsettia, photo by J. Rebman 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.

Euphorbia misera, photo courtesy of Norm Roberts 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.

Continue to Holly

Text by Jon P. Rebman, Ph.D., Curator of Botany;
Euphorbia pulcherrima, top, photo by Jon Rebman;
Euphorbia misera, bottom, photo courtesy of Norm Roberts