ADAMS TWP — The poinsettia is the Christmas season’s most popular flower. It’s no ordinary bloom — every aspect of this holiday herb tells a fascinating and unique story.

Tom McMeekin probably knows as many of the stories as anybody. McMeekin, the president of Quality Gardens at 409 Route 228, said the poinsettias in his greenhouses account for about 10 percent of annual sales.

“The poinsettias we know today originally came from a shrub in Mexico,” McMeekin said during a recent interview inside one of his greenhouses. “In nature they can grow as high as 30 feet.”

He said the most unique thing about the poinsettia is that the flower is not actually a flower. It’s “petals” are specialized leaves known as bracts.

If you look in the center of each bract, you’ll see a small berrylike growth. That’s not the flower either, but a cluster of small flowers that grows inside the berry, which is called a cyathium.

Poinsettias are constantly changing through a process the cultivation experts call selection.

Selection is not the same as hybridization, McMeekin said. That would involve cross-pollinating different varieties to come up with new shades of leaves and flowers or other traits.

Selection is different. Since new poinsettias start from cuttings of mature plants, there are no seeds to plant and no cross-pollinating. Instead, in a greenhouse full of red bracts, one of the plants might produce a white, pink or variegated bract. After this plant matures, it will provide cuttings for a new generation of the new color.

“But the new color can’t be propagated for more than a few seasons,” McMeekin said. “What that means is the varieties that existed when I started at Quality Gardens, back in 1985, those varieties no longer exist.”

But the original granddaddy of poinsettias can still be found throughout Mexico and South America.

It’s named for Joel Roberts Poinsett, the United States’ first diplomatic envoy to the Republic of Mexico from 1822 to 1830. A world traveler and avid amateur botanist, Poinsett was introduced to the flower as the “flor de noche buena,” the Christmas Eve flower.

Poinsett sent cuttings of the plant home to his South Carolina plantation and started new plants from the cuttings. By 1836 the Christmas Eve flower had become widely known as the poinsettia in the United States.

Growing poinsettias each year is a meticulous process that must be timed according to the season.

“They’re phototropic, which means they respond to the changing length of the day,” McMeekin said. “Our cuttings are propagated in June, and they spend their first few months just growing, branching and getting bigger.”

The magic happens between the dates of Sept. 15 and Oct. 23, when the shortening days and lengthening nights signal the poinsettias to slow down their growth and start forming their colorful bracts. Buds form that will turn into the cyathia.

McMeekin said Quality Gardens produces its poinsettias in a wide variety of colors and sizes. The local greenhouse takes more time in the production, which means the plants will stay healthy, hold their blooms and look nice throughout the holiday season.

Some large commercial operations are concerned with getting their plants grown and delivered before Dec. 1; then they shut down their greenhouses before winter cold jacks up their heating bill.

Several things can be done at home to prolong and life and health of poinsettias, he said.

“The first is really simple: Water it.”

When the first leaves fall off, they usually are the larger ones.

“In nature, when a plant needs water, it will sacrifice its older leaves to save the new growth,” McMeekin said. “When big leaves drop, you know it’s not getting enough.”

On the other hand, if you water too much, the plant becomes “mooshy,” he said.

When a new poinsettia goes home, the greenhouse typically will wrap it in a cellophane “sleeve” to protect it from cold and breezes. But the sleeve can trap ethylene gas, which the poinsettia naturally produces — ironically, poinsettias are sensitive to ethylene. It makes the plant wilt.

“But if you remove the sleeve, the poinsettia will perk up in a day or two,” he said.

In general, if you place the poinsettia in a sunny, relatively warm place — but not too warm — it should endure long into spring. It could even continue growing for five to seven years or longer.