The Texas Poinsettia (Poinsettia cyathophora) is a small, wild poinsettia relative showing many of the characteristics of our ornamental Christmas poinsettia, and is annual in nature. In the dry garden it makes a charming and colorful patchwork of green, scalloped alternate leaves combined with a noticeable red blotch at the base of each of the bracts (often called "petals") touching the base of the flower. It is one of the modest old-fashioned, tough plants sometimes seen in early Central Texas gardens.
The plants will grow from 1' to 3' in height, depending on access to good watering and nutrition. From midsummer till frost the innermost parts of each bract (often called the "petals") turn a vibrant red. The yellow pollen found in the clusters of small flowers (known as 'cyanthia') is very attractive to small insects as well as butterflies and some sphinx moths. Its foliage is an attractive forage for Sphinx moth caterpillars.
Texas Poinsettia is also known as Mexican Fireplant, Painted Euphorbia, Desert Poinsettia, Wild Poinsettia, Fireplant, Desert Poinsettia, Wild Poinsettia, Fire on the Mountain, Paint Leaf, Mexican Poinsettia and Kaliko plant. Texas Poinsettia and the very closely related Euphorbia heterophylla are often lumped together because they share many characteristics, but E. heterophylla, as would be suggested by its Latin name, is found with many different leaf shapes, including narrow drooping leaves without notches or scallops. One of the major differences appears to be that E. heterophylla does not "color up" and is generally regarded as a pest of crops and wastelands over the subtropical and tropical areas of the world rather than an interesting old-fashioned garden ornament. Botanical nomenclature has shifted the names of these two plants from time to time between Poinsettia and Euphorbia.
Another relative that can be found growing wild in pastures and waste places and also is sold as a garden ornamental is Snow-on-the-Mountain, Euphorbia marginata. This cream-silver-green plant has leaves beautifully margined in silver, and handsome cream-colored inflorescences. It is about 3-4 feet in height and is also quite tough and drought resistant.
Dr. Masato Yokoi of Japan has patented a form of Euphorbia (Poinsettia) cyathophora that has margins and flecks of white on the usual green leaves and has been introduced as a garden annual. It was discovered as a sport and will come true from seed.
There are several other small, green Euphorbias that are often seen in Central Texas landscapes, but their only ornamental feature is a slightly silvery cast on the tops of the plants, and no red markings at all. As would be expected for plants belonging to the Spurges, or the Euphorbia genus (which contains approximately 2,000 members), these weedy relatives have not received much attention in the landscape but are sometimes considered difficult pests of crops such as soybeans and corn.
Cultivating the Texas Poinsettia. These plants are best suited for full sun or part shade conditions, in "lean" soil that does not have extensive organic matter or fertility. Young plants will readily appear from seed after the first year, even if mulch has been applied to the flower beds. Any excess seedlings may be pulled up with little trouble. Allow 6-8" of space between plants.
All Euphorbias have milky white latex sap, which is toxic, so gardeners will need to make sure not to allow it to make contact with skin or eyes while working around the plants.