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New Mexico State University

New Mexico State University

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Poinsettias Owe Their Size, Shape to Beneficial Disease

LAS CRUCES--Potted poinsettias owe their appealing size and shape to a disease that remained a mystery until 1997, a New Mexico State University plant pathologist said.

"In most cases, a disease is negative, but in this case it's what allows the poinsettia plant to be bushy and compact," said Natalie Goldberg with NMSU's Cooperative Extension Service. "In its native habitat in Mexico and Central America, the poinsettia grows as a single stalk 10 to 12 feet tall with a small plume of red at the top."

Inside each modern poinsettia - whether red, pink or speckled - lives a biological agent called phytoplasma, which gives the plant its form, Goldberg said. Because poinsettias are grown from cuttings, the organism survives inside the plants, shaping their growth.

"This phytoplasma has probably been present since the first potted poinsettia variety was developed in 1923, but it wasn't identified until 1997, when a virus was ruled out," Goldberg said. "Phytoplasma is an organism in between bacteria and viruses that can't be grown in culture, so it's harder to identify."

Researchers transmitted phytoplasma from poinsettias to periwinkles, making the vine-like periwinkles bushy. They also found no trace of the phytoplasma in native poinsettia trees. Scientists still don't know where the organism came from or exactly how it's transmitted.

Poinsettias were first marketed as cut flowers. Growers began cultivating them as potted plants in 1923 after horticulturist Paul Ecke developed a short variety with multiple branches. His poinsettias produced more "flowers" - actually red leaves or bracts - and retained them longer. Since then, poinsettias have become one of the most important U.S. horticultural crops, valued at $325 million in 1997.

The poinsettia's holiday history dates back to the 17th century, when Franciscan priests used the red flowers in nativity processions. Joel Robert Poinsett, a biologist and the first U.S. ambassador to Mexico, brought the plant to the United States in 1825.