In the six weeks leading up to Christmas, one plant seems to come out of the woodwork to redefine the whole festive landscape.

The red and green poinsettia is as timeless as Bing Crosby crooning “White Christmas,” though the appearance of more than 30 million plants is anything but automatic. Since the spring, skilled but nervous growers across the land have been raising one of their most economically important, and finicky, crops.

This is only one aspect of poinsettia dynamics. Since a canny California cut-flower grower named Paul Ecke Sr. came up with the idea of the poinsettia as a potted plant for the holidays, breeders have been trying to perfect it.

Some of the shifts have been aesthetic: decorator poinsettias in lime green, ivory or burgundy, poinsettias whose petal-like bracts are flecked, marbled, splashed and otherwise turned into something that will spur your Aunt Mabel to wonder what they will think of next.

The rare dogwood poinsettia, one of the parents of the new hybrids creating a buzz. (Adrian Higgins/The Washington Post)

Other breeding improvements are not obvious to consumers but critical to growers and retailers in the way the plant can be grown and shipped and hold up outside the greenhouse.

As recently as 20 years ago or so, poinsettias were seen as the plant you hoped would not break apart or drop most of its leaves before Santa arrived.

But over the past two to three years, consumers have seen a conspicuous shift in the look of the poinsettia. The classic ebullient poinsettias still predominate, especially the reds, but you may notice some curiously different plants. They are smaller and more compact but effervescent with spear-shaped petals that appear in whorls layered one on top of the other. (Poinsettia “flowers” are botanically bracts that surround the true flowers.) The range of varieties is still limited — more are in the works — but already they are available in both soft and vivid pinks, the latter with a neon glow. They’re so hot, they’re cool.

Another significant color shift is in a white variety named Princettia Pure White. It is a clear bone white, unlike the creamy whites of other poinsettias. It is a tint that poinsettia breeders have been chasing for decades.

To date, all poinsettias were derived from a single species found in western Mexico named Euphorbia pulcherrima. This grows into a tall, rangy shrub whose scarlet bracts appear in the winter.

The smaller and floriferous new varieties are hybrids between this species and another, a summer bloomer named the dogwood poinsettia (Euphorbia cornastra). Rarely seen, either in the wild or in cultivation, specimens were collected from Mexico in the early 1990s by graduate students at the University of Texas. One of them was Alice Le Duc, who saw the potential value of the clear white flowers in crossbreeding with the Christmas poinsettia, and she passed some of her stock to the breeders at the Ecke Ranch. (The company has since been sold to a European breeder, Dümmen Orange, but maintains its own breeding program.) The new hybrids are now reaching consumers in three separate brands: Princettia, from Suntory Flowers; Luv U Pink, from the Paul Ecke Ranch; and J'Adore, from Dümmen Orange.

John Dole, who coordinates North Carolina State University's poinsettia trials program, sees the hybrids as a milestone in the history of the poinsettia. "It's pretty major, and it could be on a par with some of the other breakthroughs," he said. These include poinsettias that hold their leaves and grow bushy without having to pinch stems.

The parentage allows the creation of a clear white poinsettia, here Princettia Pure White. (Adrian Higgins/The Washington Post)

You can view these hybrids at the U.S. Botanic Garden conservatory at 100 Maryland Ave. SW, where a rear gallery is devoted to a gently didactic exhibition of the history of the poinsettia in U.S. floriculture. The display in the South Transition is part of the "Season's Greenings" holiday exhibit, which runs through Jan. 1.

The wild Christmas poinsettia is now hard to find in the United States, so plant curator William McLaughlin has bred his own crosses to approximate it, with several specimens in red bloom and one in white. Visitors get to see what the wildling looks like, a tall, leggy bush with bract clusters isolated at the end of long branches. This gives measure to how far the breeders and growers have come in producing the poinsettias in the 21st century.

A dogwood poinsettia that McLaughlin grew from seed he received from Le Duc is central to the exhibit, though it looks pretty prosaic — a lanky vase-shaped shrub with small white bract clusters. Ironically, it is the rarest plant in the room. There are far fewer specimens of this in botanic gardens than the much-hyped corpse flower, which always draws TV cameras and crowds.

The exhibit also includes now-dated poinsettia varieties that represented advances through the years. One is called Annette Hegg, the first self-branching type. Another is Oak Leaf, one of the first to hold its leaves. But the ones getting the attention from visitors are the new hybrids. “People say, ‘How do you get so many bracts?’ and we say, ‘That’s how the plant grows,’ ” said Devin Dotson, the botanic garden’s spokesman. This trait results from the plants’ sterility, bestowed by the unnatural parentage. The true flowers fail to develop and fall off.

The exhibit features four Princettia hybrids and three Luv U Pink ones.

Le Duc, who now teaches at Texas State University, said a well-grown plant in the house could keep blooming until April. It is this stamina and the strong pink colors that prompted Dümmen Orange to pitch the hybrids in Europe as a plant for the Valentine’s Day and Easter markets. This hasn’t been successful to date. It seems breeders will have to work on more red varieties if the hybrids are to reach their Yuletide potential. The only red I saw at the show was Princettia Red, a darker shade of magenta. One asset these hybrids have is a rich dark-green leaf, a highly desirable trait in poinsettias and one bestowed here by the dogwood poinsettia parentage.

Meanwhile, the conveyor belt of traditional poinsettia breeding continues to whir along.

Gary Vollmer, product manager for Selecta Poinsettias, said his company is focusing on improving traditional red varieties. The problem with many of the trendy crimson and maroon varieties is that they fade gray, he said. “Our goal is to get that saturated red but not by bringing in blue,” he said. Instead it is achieved by breeding to increase the red pigmentation in the layers of bract cells. (This is all done by traditional selective breeding, not with genetically modified organisms.) “If you put enough pigment in there and make it dense enough, it shifts toward the crimson,” he said.

An example, he said, is the company’s Christmas Beauty Red, which came to market two years ago. “It’s not a traditional dark red,” he said. “It’s just really, really red.”

Vollmer sees two encouraging trends in the marketplace. A decade ago, poinsettias were swept up in the retailers’ drive to start the holiday sales season earlier in November. Poinsettia shipments suggest the season is shifting back to December.

The other change is a move away from using the poinsettia as a loss leader. “If the consumer sees it as a 99-cent giveaway on Black Friday, or a beautiful $11.99 gift item in the floral department, that’s a different value equation,” he said. “And I think the retailers are tired of losing money on the giveaways.”

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