Euphorbia pulcherrima has come a long way since Joel R. Poinsett brought some home to his plantation in South Carolina from Taxco, in Mexico, 160 years ago. But the global acceptance of poinsettias as a symbol of Christmas owes more to a family-run horticultural ranch in Encinitas, Calif., than to Poinsett, the first U.S. ambassador to Mexico, who made the introductions.

The Paul Ecke Poinsettia Ranch, about 30 miles north of San Diego, claims without challenge to be the starting point for about 90 percent of the flowering poinsettias of the world, producing each Christmas a half-million flowering plants for the California and Arizona florist trade and shipping millions of cuttings around the world to provide the basic stock of national and international production. Despite the short sales season, largely limited to the six weeks before Christmas, poinsettias now rank No. 1 nationally in the dollar value of potted flowering plants - ahead of chrysanthemums and geraniums.Prime plants on the market today bear little resemblance to the plant that was cultivated by the Aztecs and called Cuetlaxochitle. The fragile, pale, rangy plants in the wild - often characterized by premature leaf drop and a short flowering - have been succeeded by new generations in an intensive and on-going breeding program that began in 1920 under the direction of Paul Ecke Sr., now 93.

It takes at least three years from new seedling to proven plant before the new poinsettias are introduced to major market testing. The process, however tedious, pays off, he emphasized. He could prove the point with his newest introduction, Eckespoint Lilo, with its ruby bracts, deep-green foliage and unusual ability to survive hostile environments.

Montezuma would not have recognized it - nor, for that matter, Ambassador Poinsett.